Device and method for scalable coding of video information

ABSTRACT

An apparatus may include a memory configured to store video data associated with a reference layer (RL) and an enhancement layer (EL) and a processor in communication with the memory. The processor may determine whether a first enhancement layer (EL) picture associated with a first parameter set is an intra random access point (IRAP) picture, determine whether a first access unit including the EL picture immediately follows a splice point, and perform one of (1) refraining from associating the first EL picture with a second parameter set different from the first parameter set, or (2) associating the first EL picture with a second parameter set different from the first parameter set. The processor may encode or decode the video data.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional No. 61/891,264,filed Oct. 15, 2013.

TECHNICAL FIELD

This disclosure relates to the field of video coding and compression,particularly to scalable video coding (SVC), multiview video coding(MVC), or 3D video coding (3DV).

BACKGROUND

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, digital direct broadcastsystems, wireless broadcast systems, personal digital assistants (PDAs),laptop or desktop computers, digital cameras, digital recording devices,digital media players, video gaming devices, video game consoles,cellular or satellite radio telephones, video teleconferencing devices,and the like. Digital video devices implement video compressiontechniques, such as those described in the standards defined by MPEG-2,MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced Video Coding(AVC), the High Efficiency Video Coding (HEVC) standard presently underdevelopment, and extensions of such standards. The video devices maytransmit, receive, encode, decode, and/or store digital videoinformation more efficiently by implementing such video codingtechniques.

Video compression techniques perform spatial (intra-picture) predictionand/or temporal (inter-picture) prediction to reduce or removeredundancy inherent in video sequences. For block-based video coding, avideo slice (e.g., a video frame, a portion of a video frame, etc.) maybe partitioned into video blocks, which may also be referred to astreeblocks, coding units (CUs) and/or coding nodes. Video blocks in anintra-coded (I) slice of a picture are encoded using spatial predictionwith respect to reference samples in neighboring blocks in the samepicture. Video blocks in an inter-coded (P or B) slice of a picture mayuse spatial prediction with respect to reference samples in neighboringblocks in the same picture or temporal prediction with respect toreference samples in other reference pictures. Pictures may be referredto as frames, and reference pictures may be referred to as referenceframes.

Spatial or temporal prediction results in a predictive block for a blockto be coded. Residual data represents pixel differences between theoriginal block to be coded and the predictive block. An inter-codedblock is encoded according to a motion vector that points to a block ofreference samples forming the predictive block, and the residual dataindicating the difference between the coded block and the predictiveblock. An intra-coded block is encoded according to an intra-coding modeand the residual data. For further compression, the residual data may betransformed from the pixel domain to a transform domain, resulting inresidual transform coefficients, which then may be quantized. Thequantized transform coefficients, initially arranged in atwo-dimensional array, may be scanned in order to produce aone-dimensional vector of transform coefficients, and entropy encodingmay be applied to achieve even more compression.

SUMMARY

Scalable video coding (SVC) refers to video coding in which a base layer(BL), sometimes referred to as a reference layer (RL), and one or morescalable enhancement layers (ELs) are used. In SVC, the base layer cancarry video data with a base level of quality. The one or moreenhancement layers can carry additional video data to support, forexample, higher spatial, temporal, and/or signal-to-noise (SNR) levels.Enhancement layers may be defined relative to a previously encodedlayer. For example, a bottom layer may serve as a BL, while a top layermay serve as an EL. Middle layers may serve as either ELs or RLs, orboth. For example, a middle layer (e.g., a layer that is neither thelowest layer nor the highest layer) may be an EL for the layers belowthe middle layer, such as the base layer or any intervening enhancementlayers, and at the same time serve as a RL for one or more enhancementlayers above the middle layer. Similarly, in the Multiview or 3Dextension of the HEVC standard, there may be multiple views, andinformation of one view may be utilized to code (e.g., encode or decode)the information of another view (e.g., motion estimation, motion vectorprediction and/or other redundancies).

In SVC, the parameters used by the encoder or the decoder are groupedinto parameter sets based on the coding level (e.g., video-level,sequence-level, picture-level, slice level, etc.) in which they may beutilized. For example, parameters that may be utilized by one or morecoded video sequences in the bitstream may be included in a videoparameter set (VPS), and parameters that are utilized by one or morepictures in a coded video sequence may be included in a sequenceparameter set (SPS). Similarly, parameters that are utilized by one ormore slices in a picture may be included in a picture parameter set(PPS), and other parameters that are specific to a single slice may beincluded in a slice header. Similarly, the indication of which parameterset(s) a particular layer is using at a given time may be provided atvarious coding levels. For example, if the slice header of a slice inthe particular layer refers to a PPS, the PPS is activated for the sliceor the picture containing the slice. Similarly, if the PPS refers to anSPS, the SPS is activated for the picture or the coded video sequencecontaining the picture, and if the SPS refers to a VPS, the VPS isactivated for the coded video sequence or the video layer containing thecoded video sequence.

Typically, a parameter set remains active (e.g., is currently being usedfor decoding a particular segment of the bitstream) for the entirecoding level at which the parameter set is utilized. For example, anactivated SPS may remain active for the entire sequence that initiallyactivated the SPS, and an activated PPS may remain active for the entirepicture that initially activated the PPS. However, in some existingcoding schemes, a parameter set may be activated in the middle of thecoding level at which another parameter set is currently active. In sucha case, some of the parameters (e.g., picture resolution) that shouldremain constant for the duration of the coding process of the particularcoding level (e.g., sequence, picture, slice, etc.) may be altered bythe activation of the new parameter set and may result in undesiredoutcomes.

Thus, a coding scheme that manages the activation of parameter sets moreefficiently and thereby improves coding accuracy and error resilience isdesired.

The systems, methods and devices of this disclosure each have severalinnovative aspects, no single one of which is solely responsible for thedesirable attributes disclosed herein.

In one aspect, an apparatus configured to code (e.g., encode or decode)video information includes a memory unit and a processor incommunication with the memory unit. The memory unit is configured tostore video information associated with a reference layer (RL) and anenhancement layer (EL), the RL having an RL picture in a first accessunit, and the EL having a first EL picture in the first access unit,wherein the first EL picture is associated with a first set ofparameters. The processor is configured to determine whether the firstEL picture is an intra random access point (IRAP) picture, determinewhether the first access unit immediately follows a splice point wherefirst video information is joined with second video informationincluding the first EL picture, and perform, based on the determinationof whether the first EL picture is an intra random access point (IRAP)picture and whether the first access unit immediately follows a splicepoint, one of (1) refraining from associating the first EL picture witha second set of parameters that is different from the first set ofparameters, or (2) associating the first EL picture with a second set ofparameters that is different from the first set of parameters.

In another aspect, a method of encoding video information comprisesdetermining whether a first enhancement layer (EL) picture in a firstaccess unit of an EL is an intra random access point (IRAP) picture, thefirst EL picture associated with a first set of parameters, determiningwhether the first access unit immediately follows a splice point wherefirst video information is joined with second video informationincluding the first EL picture, and performing, based on thedetermination of whether the first EL picture is an intra random accesspoint (IRAP) picture and whether the first access unit immediatelyfollows a splice point, one of (1) refraining from associating the firstEL picture with a second set of parameters that is different from thefirst set of parameters, or (2) associating the first EL picture with asecond set of parameters that is different from the first set ofparameters.

In another aspect, a non-transitory computer readable medium comprisescode that, when executed, causes an apparatus to perform a process. Theprocess includes storing video information associated with a referencelayer (RL) and an enhancement layer (EL), the RL having an RL picture ina first access unit, and the EL having a first EL picture in the firstaccess unit, wherein the first EL picture is associated with a first setof parameters, determining whether the first EL picture is an intrarandom access point (IRAP) picture, determining whether the first accessunit immediately follows a splice point where first video information isjoined with second video information including the first EL picture, andperforming, based on the determination of whether the first EL pictureis an intra random access point (IRAP) picture and whether the firstaccess unit immediately follows a splice point, one of (1) refrainingfrom associating the first EL picture with a second set of parametersthat is different from the first set of parameters, or (2) associatingthe first EL picture with a second set of parameters that is differentfrom the first set of parameters.

In another aspect, a video coding device configured to code videoinformation comprises means for storing video information associatedwith a reference layer (RL) and an enhancement layer (EL), the RL havingan RL picture in a first access unit, and the EL having a first ELpicture in the first access unit, wherein the first EL picture isassociated with a first set of parameters, means for determining whetherthe first EL picture is an intra random access point (IRAP) picture,means for determining whether the first access unit immediately followsa splice point where first video information is joined with second videoinformation including the first EL picture, and means for performing,based on the determination of whether the first EL picture is an intrarandom access point (IRAP) picture and whether the first access unitimmediately follows a splice point, one of (1) refraining fromassociating the first EL picture with a second set of parameters that isdifferent from the first set of parameters, or (2) associating the firstEL picture with a second set of parameters that is different from thefirst set of parameters.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a block diagram illustrating an example video encoding anddecoding system that may utilize techniques in accordance with aspectsdescribed in this disclosure.

FIG. 1B is a block diagram illustrating another example video encodingand decoding system that may perform techniques in accordance withaspects described in this disclosure.

FIG. 2A is a block diagram illustrating an example of a video encoderthat may implement techniques in accordance with aspects described inthis disclosure.

FIG. 2B is a block diagram illustrating an example of a video encoderthat may implement techniques in accordance with aspects described inthis disclosure.

FIG. 3A is a block diagram illustrating an example of a video decoderthat may implement techniques in accordance with aspects described inthis disclosure.

FIG. 3B is a block diagram illustrating an example of a video decoderthat may implement techniques in accordance with aspects described inthis disclosure.

FIG. 4 is a block diagram illustrating an example configuration ofpictures in different layers, according to one embodiment of the presentdisclosure.

FIG. 5 illustrates a flow chart illustrating a method of coding videoinformation, according to one embodiment of the present disclosure.

DETAILED DESCRIPTION

Certain embodiments described herein relate to inter-layer predictionfor scalable video coding in the context of advanced video codecs, suchas HEVC (High Efficiency Video Coding). More specifically, the presentdisclosure relates to systems and methods for improved performance ofinter-layer prediction in scalable video coding (SVC) extension of HEVC.

In the description below, H.264/AVC techniques related to certainembodiments are described; the HEVC standard and related techniques arealso discussed. While certain embodiments are described herein in thecontext of the HEVC and/or H.264 standards, one having ordinary skill inthe art may appreciate that systems and methods disclosed herein may beapplicable to any suitable video coding standard. For example,embodiments disclosed herein may be applicable to one or more of thefollowing standards: ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-T H.262 orISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual and ITU-TH.264 (also known as ISO/IEC MPEG-4 AVC), including its Scalable VideoCoding (SVC) and Multiview Video Coding (MVC) extensions.

HEVC generally follows the framework of previous video coding standardsin many respects. The unit of prediction in HEVC is different from thatin certain previous video coding standards (e.g., macroblock). In fact,the concept of macroblock does not exist in HEVC as understood incertain previous video coding standards. Macroblock is replaced by ahierarchical structure based on a quadtree scheme, which may providehigh flexibility, among other possible benefits. For example, within theHEVC scheme, three types of blocks, Coding Unit (CU), Prediction Unit(PU), and Transform Unit (TU), are defined. CU may refer to the basicunit of region splitting. CU may be considered analogous to the conceptof macroblock, but HEVC does not restrict the maximum size of CUs andmay allow recursive splitting into four equal size CUs to improve thecontent adaptivity. PU may be considered the basic unit of inter/intraprediction, and a single PU may contain multiple arbitrary shapepartitions to effectively code irregular image patterns. TU may beconsidered the basic unit of transform. TU can be defined independentlyfrom the PU; however, the size of a TU may be limited to the size of theCU to which the TU belongs. This separation of the block structure intothree different concepts may allow each unit to be optimized accordingto the respective role of the unit, which may result in improved codingefficiency.

For purposes of illustration only, certain embodiments disclosed hereinare described with examples including only two layers (e.g., a lowerlayer such as the base layer, and a higher layer such as the enhancementlayer). It should be understood that such examples may be applicable toconfigurations including multiple base and/or enhancement layers. Inaddition, for ease of explanation, the following disclosure includes theterms “frames” or “blocks” with reference to certain embodiments.However, these terms are not meant to be limiting. For example, thetechniques described below can be used with any suitable video units,such as blocks (e.g., CU, PU, TU, macroblocks, etc.), slices, frames,etc.

Video Coding Standards

A digital image, such as a video image, a TV image, a still image or animage generated by a video recorder or a computer, may consist of pixelsor samples arranged in horizontal and vertical lines. The number ofpixels in a single image is typically in the tens of thousands. Eachpixel typically contains luminance and chrominance information. Withoutcompression, the sheer quantity of information to be conveyed from animage encoder to an image decoder would render real-time imagetransmission impossible. To reduce the amount of information to betransmitted, a number of different compression methods, such as JPEG,MPEG and H.263 standards, have been developed.

Video coding standards include ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-TH.262 or ISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual andITU-T H.264 (also known as ISO/IEC MPEG-4 AVC), including its ScalableVideo Coding (SVC) and Multiview Video Coding (MVC) extensions.

In addition, a new video coding standard, namely High Efficiency VideoCoding (HEVC), is being developed by the Joint Collaboration Team onVideo Coding (JCT-VC) of ITU-T Video Coding Experts Group (VCEG) andISO/IEC Motion Picture Experts Group (MPEG). The full citation for theHEVC Draft 10 is document JCTVC-L1003, Bross et al., “High EfficiencyVideo Coding (HEVC) Text Specification Draft 10,” Joint CollaborativeTeam on Video Coding (JCT-VC) of ITU-T SG16 WP3 and ISO/IECJTC1/SC29/WG11, 12th Meeting: Geneva, Switzerland, Jan. 14, 2013 to Jan.23, 2013. The multiview extension to HEVC, namely MV-HEVC, and thescalable extension to HEVC, named SHVC, are also being developed by theJCT-3V (ITU-T/ISO/IEC Joint Collaborative Team on 3D Video CodingExtension Development) and JCT-VC, respectively.

Various aspects of the novel systems, apparatuses, and methods aredescribed more fully hereinafter with reference to the accompanyingdrawings. This disclosure may, however, be embodied in many differentforms and should not be construed as limited to any specific structureor function presented throughout this disclosure. Rather, these aspectsare provided so that this disclosure will be thorough and complete, andwill fully convey the scope of the disclosure to those skilled in theart. Based on the teachings herein one skilled in the art shouldappreciate that the scope of the disclosure is intended to cover anyaspect of the novel systems, apparatuses, and methods disclosed herein,whether implemented independently of, or combined with, any other aspectof the present disclosure. For example, an apparatus may be implementedor a method may be practiced using any number of the aspects set forthherein. In addition, the scope of the present disclosure is intended tocover such an apparatus or method which is practiced using otherstructure, functionality, or structure and functionality in addition toor other than the various aspects of the present disclosure set forthherein. It should be understood that any aspect disclosed herein may beembodied by one or more elements of a claim.

Although particular aspects are described herein, many variations andpermutations of these aspects fall within the scope of the disclosure.Although some benefits and advantages of the preferred aspects arementioned, the scope of the disclosure is not intended to be limited toparticular benefits, uses, or objectives. Rather, aspects of thedisclosure are intended to be broadly applicable to different wirelesstechnologies, system configurations, networks, and transmissionprotocols, some of which are illustrated by way of example in thefigures and in the following description of the preferred aspects. Thedetailed description and drawings are merely illustrative of thedisclosure rather than limiting, the scope of the disclosure beingdefined by the appended claims and equivalents thereof.

The attached drawings illustrate examples. Elements indicated byreference numbers in the attached drawings correspond to elementsindicated by like reference numbers in the following description. Inthis disclosure, elements having names that start with ordinal words(e.g., “first,” “second,” “third,” and so on) do not necessarily implythat the elements have a particular order. Rather, such ordinal wordsare merely used to refer to different elements of a same or similartype.

Video Coding System

FIG. 1A is a block diagram that illustrates an example video codingsystem 10 that may utilize techniques in accordance with aspectsdescribed in this disclosure. As used described herein, the term “videocoder” refers generically to both video encoders and video decoders. Inthis disclosure, the terms “video coding” or “coding” may refergenerically to video encoding and video decoding. In addition to videoencoders and video decoders, the aspects described in the presentapplication may be extended to other related devices such as transcoders(e.g., devices that can decode a bitstream and re-encode anotherbitstream) and middleboxes (e.g., devices that can modify, transform,and/or otherwise manipulate a bitstream).

As shown in FIG. 1A, video coding system 10 includes a source module 12that generates encoded video data to be decoded at a later time by adestination module 14. In the example of FIG. 1A, the source module 12and destination module 14 are on separate devices—specifically, thesource module 12 is part of a source device, and the destination module14 is part of a destination device. It is noted, however, that thesource and destination modules 12, 14 may be on or part of the samedevice, as shown in the example of FIG. 1B.

With reference once again, to FIG. 1A, the source module 12 and thedestination module 14 may comprise any of a wide range of devices,including desktop computers, notebook (e.g., laptop) computers, tabletcomputers, set-top boxes, telephone handsets such as so-called “smart”phones, so-called “smart” pads, televisions, cameras, display devices,digital media players, video gaming consoles, video streaming device, orthe like. In some cases, the source module 12 and the destination module14 may be equipped for wireless communication.

The destination module 14 may receive the encoded video data to bedecoded via a link 16. The link 16 may comprise any type of medium ordevice capable of moving the encoded video data from the source module12 to the destination module 14. In the example of FIG. 1A, the link 16may comprise a communication medium to enable the source module 12 totransmit encoded video data directly to the destination module 14 inreal-time. The encoded video data may be modulated according to acommunication standard, such as a wireless communication protocol, andtransmitted to the destination module 14. The communication medium maycomprise any wireless or wired communication medium, such as a radiofrequency (RF) spectrum or one or more physical transmission lines. Thecommunication medium may form part of a packet-based network, such as alocal area network, a wide-area network, or a global network such as theInternet. The communication medium may include routers, switches, basestations, or any other equipment that may be useful to facilitatecommunication from the source module 12 to the destination module 14.

Alternatively, encoded data may be output from an output interface 22 toan optional storage device 31. Similarly, encoded data may be accessedfrom the storage device 31 by an input interface 28. The storage device31 may include any of a variety of distributed or locally accessed datastorage media such as a hard drive, flash memory, volatile ornon-volatile memory, or any other suitable digital storage media forstoring encoded video data. In a further example, the storage device 31may correspond to a file server or another intermediate storage devicethat may hold the encoded video generated by the source module 12. Thedestination module 14 may access stored video data from the storagedevice 31 via streaming or download. The file server may be any type ofserver capable of storing encoded video data and transmitting thatencoded video data to the destination module 14. Example file serversinclude a web server (e.g., for a website), an FTP server, networkattached storage (NAS) devices, or a local disk drive. The destinationmodule 14 may access the encoded video data through any standard dataconnection, including an Internet connection. This may include awireless channel (e.g., a Wi-Fi connection), a wired connection (e.g.,DSL, cable modem, etc.), or a combination of both that is suitable foraccessing encoded video data stored on a file server. The transmissionof encoded video data from the storage device 31 may be a streamingtransmission, a download transmission, or a combination of both.

The techniques of this disclosure are not limited to wirelessapplications or settings. The techniques may be applied to video codingin support of any of a variety of multimedia applications, such asover-the-air television broadcasts, cable television transmissions,satellite television transmissions, streaming video transmissions, e.g.,via the Internet (e.g., dynamic adaptive streaming over HTTP (DASH),etc.), encoding of digital video for storage on a data storage medium,decoding of digital video stored on a data storage medium, or otherapplications. In some examples, video coding system 10 may be configuredto support one-way or two-way video transmission to support applicationssuch as video streaming, video playback, video broadcasting, and/orvideo telephony.

In the example of FIG. 1A, the source module 12 includes a video source18, video encoder 20 and an output interface 22. In some cases, theoutput interface 22 may include a modulator/demodulator (modem) and/or atransmitter. In the source module 12, the video source 18 may include asource such as a video capture device, e.g., a video camera, a videoarchive containing previously captured video, a video feed interface toreceive video from a video content provider, and/or a computer graphicssystem for generating computer graphics data as the source video, or acombination of such sources. As one example, if the video source 18 is avideo camera, the source module 12 and the destination module 14 mayform so-called camera phones or video phones, as illustrated in theexample of FIG. 1B. However, the techniques described in this disclosuremay be applicable to video coding in general, and may be applied towireless and/or wired applications.

The captured, pre-captured, or computer-generated video may be encodedby the video encoder 20. The encoded video data may be transmitteddirectly to the destination module 14 via the output interface 22 of thesource module 12. The encoded video data may also (or alternatively) bestored onto the storage device 31 for later access by the destinationmodule 14 or other devices, for decoding and/or playback. The videoencoder 20 illustrated in FIGS. 1A and 1B may comprise the video encoder20 illustrated FIG. 2A, the video encoder 23 illustrated in FIG. 2B, orany other video encoder described herein.

In the example of FIG. 1A, the destination module 14 includes an inputinterface 28, a video decoder 30, and a display device 32. In somecases, the input interface 28 may include a receiver and/or a modem. Theinput interface 28 of the destination module 14 may receive the encodedvideo data over the link 16. The encoded video data communicated overthe link 16, or provided on the storage device 31, may include a varietyof syntax elements generated by the video encoder 20 for use by a videodecoder, such as the video decoder 30, in decoding the video data. Suchsyntax elements may be included with the encoded video data transmittedon a communication medium, stored on a storage medium, or stored a fileserver. The video decoder 30 illustrated in FIGS. 1A and 1B may comprisethe video decoder 30 illustrated FIG. 3A, the video decoder 33illustrated in FIG. 3B, or any other video decoder described herein.

The display device 32 may be integrated with, or external to, thedestination module 14. In some examples, the destination module 14 mayinclude an integrated display device and also be configured to interfacewith an external display device. In other examples, the destinationmodule 14 may be a display device. In general, the display device 32displays the decoded video data to a user, and may comprise any of avariety of display devices such as a liquid crystal display (LCD), aplasma display, an organic light emitting diode (OLED) display, oranother type of display device.

In related aspects, FIG. 1B shows an example video encoding and decodingsystem 10′ wherein the source and destination modules 12, 14 are on orpart of a device or user device 11. The device 11 may be a telephonehandset, such as a “smart” phone or the like. The device 11 may includean optional controller/processor module 13 in operative communicationwith the source and destination modules 12, 14. The system 10′ of FIG.1B may further include a video processing unit 21 between the videoencoder 20 and the output interface 22. In some implementations, thevideo processing unit 21 is a separate unit, as illustrated in FIG. 1B;however, in other implementations, the video processing unit 21 can beimplemented as a portion of the video encoder 20 and/or theprocessor/controller module 13. The system 10′ may also include anoptional tracker 29, which can track an object of interest in a videosequence. The object or interest to be tracked may be segmented by atechnique described in connection with one or more aspects of thepresent disclosure. In related aspects, the tracking may be performed bythe display device 32, alone or in conjunction with the tracker 29. Thesystem 10′ of FIG. 1B, and components thereof, are otherwise similar tothe system 10 of FIG. 1A, and components thereof.

Video encoder 20 and video decoder 30 may operate according to a videocompression standard, such as the High Efficiency Video Coding (HEVC)standard presently under development, and may conform to a HEVC TestModel (HM). Alternatively, video encoder 20 and video decoder 30 mayoperate according to other proprietary or industry standards, such asthe ITU-T H.264 standard, alternatively referred to as MPEG-4, Part 10,Advanced Video Coding (AVC), or extensions of such standards. Thetechniques of this disclosure, however, are not limited to anyparticular coding standard. Other examples of video compressionstandards include MPEG-2 and ITU-T H.263.

Although not shown in the examples of FIGS. 1A and 1B, video encoder 20and video decoder 30 may each be integrated with an audio encoder anddecoder, and may include appropriate MUX-DEMUX units, or other hardwareand software, to handle encoding of both audio and video in a commondata stream or separate data streams. If applicable, in some examples,MUX-DEMUX units may conform to the ITU H.223 multiplexer protocol, orother protocols such as the user datagram protocol (UDP).

The video encoder 20 and the video decoder 30 each may be implemented asany of a variety of suitable encoder circuitry, such as one or moremicroprocessors, digital signal processors (DSPs), application specificintegrated circuits (ASICs), field programmable gate arrays (FPGAs),discrete logic, software, hardware, firmware or any combinationsthereof. When the techniques are implemented partially in software, adevice may store instructions for the software in a suitable,non-transitory computer-readable medium and execute the instructions inhardware using one or more processors to perform the techniques of thisdisclosure. Each of the video encoder 20 and the video decoder 30 may beincluded in one or more encoders or decoders, either of which may beintegrated as part of a combined encoder/decoder (CODEC) in a respectivedevice.

Video Coding Process

As mentioned briefly above, video encoder 20 encodes video data. Thevideo data may comprise one or more pictures. Each of the pictures is astill image forming part of a video. In some instances, a picture may bereferred to as a video “frame.” When video encoder 20 encodes the videodata, video encoder 20 may generate a bitstream. The bitstream mayinclude a sequence of bits that form a coded representation of the videodata. The bitstream may include coded pictures and associated data. Acoded picture is a coded representation of a picture.

To generate the bitstream, video encoder 20 may perform encodingoperations on each picture in the video data. When video encoder 20performs encoding operations on the pictures, video encoder 20 maygenerate a series of coded pictures and associated data. The associateddata may include video parameter sets (VPS), sequence parameter sets,picture parameter sets, adaptation parameter sets, and other syntaxstructures. A sequence parameter set (SPS) may contain parametersapplicable to zero or more sequences of pictures. A picture parameterset (PPS) may contain parameters applicable to zero or more pictures. Anadaptation parameter set (APS) may contain parameters applicable to zeroor more pictures. Parameters in an APS may be parameters that are morelikely to change than parameters in a PPS.

To generate a coded picture, video encoder 20 may partition a pictureinto equally-sized video blocks. A video block may be a two-dimensionalarray of samples. Each of the video blocks is associated with atreeblock. In some instances, a treeblock may be referred to as alargest coding unit (LCU). The treeblocks of HEVC may be broadlyanalogous to the macroblocks of previous standards, such as H.264/AVC.However, a treeblock is not necessarily limited to a particular size andmay include one or more coding units (CUs). Video encoder 20 may usequadtree partitioning to partition the video blocks of treeblocks intovideo blocks associated with CUs, hence the name “treeblocks.”

In some examples, video encoder 20 may partition a picture into aplurality of slices. Each of the slices may include an integer number ofCUs. In some instances, a slice comprises an integer number oftreeblocks. In other instances, a boundary of a slice may be within atreeblock.

As part of performing an encoding operation on a picture, video encoder20 may perform encoding operations on each slice of the picture. Whenvideo encoder 20 performs an encoding operation on a slice, videoencoder 20 may generate encoded data associated with the slice. Theencoded data associated with the slice may be referred to as a “codedslice.”

To generate a coded slice, video encoder 20 may perform encodingoperations on each treeblock in a slice. When video encoder 20 performsan encoding operation on a treeblock, video encoder 20 may generate acoded treeblock. The coded treeblock may comprise data representing anencoded version of the treeblock.

When video encoder 20 generates a coded slice, video encoder 20 mayperform encoding operations on (e.g., encode) the treeblocks in theslice according to a raster scan order. For example, video encoder 20may encode the treeblocks of the slice in an order that proceeds fromleft to right across a topmost row of treeblocks in the slice, then fromleft to right across a next lower row of treeblocks, and so on untilvideo encoder 20 has encoded each of the treeblocks in the slice.

As a result of encoding the treeblocks according to the raster scanorder, the treeblocks above and to the left of a given treeblock mayhave been encoded, but treeblocks below and to the right of the giventreeblock have not yet been encoded. Consequently, video encoder 20 maybe able to access information generated by encoding treeblocks above andto the left of the given treeblock when encoding the given treeblock.However, video encoder 20 may be unable to access information generatedby encoding treeblocks below and to the right of the given treeblockwhen encoding the given treeblock.

To generate a coded treeblock, video encoder 20 may recursively performquadtree partitioning on the video block of the treeblock to divide thevideo block into progressively smaller video blocks. Each of the smallervideo blocks may be associated with a different CU. For example, videoencoder 20 may partition the video block of a treeblock into fourequally-sized sub-blocks, partition one or more of the sub-blocks intofour equally-sized sub-sub-blocks, and so on. A partitioned CU may be aCU whose video block is partitioned into video blocks associated withother CUs. A non-partitioned CU may be a CU whose video block is notpartitioned into video blocks associated with other CUs.

One or more syntax elements in the bitstream may indicate a maximumnumber of times video encoder 20 may partition the video block of atreeblock. A video block of a CU may be square in shape. The size of thevideo block of a CU (e.g., the size of the CU) may range from 8×8 pixelsup to the size of a video block of a treeblock (e.g., the size of thetreeblock) with a maximum of 64×64 pixels or greater.

Video encoder 20 may perform encoding operations on (e.g., encode) eachCU of a treeblock according to a z-scan order. In other words, videoencoder 20 may encode a top-left CU, a top-right CU, a bottom-left CU,and then a bottom-right CU, in that order. When video encoder 20performs an encoding operation on a partitioned CU, video encoder 20 mayencode CUs associated with sub-blocks of the video block of thepartitioned CU according to the z-scan order. In other words, videoencoder 20 may encode a CU associated with a top-left sub-block, a CUassociated with a top-right sub-block, a CU associated with abottom-left sub-block, and then a CU associated with a bottom-rightsub-block, in that order.

As a result of encoding the CUs of a treeblock according to a z-scanorder, the CUs above, above-and-to-the-left, above-and-to-the-right,left, and below-and-to-the left of a given CU may have been encoded. CUsbelow and to the right of the given CU have not yet been encoded.Consequently, video encoder 20 may be able to access informationgenerated by encoding some CUs that neighbor the given CU when encodingthe given CU. However, video encoder 20 may be unable to accessinformation generated by encoding other CUs that neighbor the given CUwhen encoding the given CU.

When video encoder 20 encodes a non-partitioned CU, video encoder 20 maygenerate one or more prediction units (PUs) for the CU. Each of the PUsof the CU may be associated with a different video block within thevideo block of the CU. Video encoder 20 may generate a predicted videoblock for each PU of the CU. The predicted video block of a PU may be ablock of samples. Video encoder 20 may use intra prediction or interprediction to generate the predicted video block for a PU.

When video encoder 20 uses intra prediction to generate the predictedvideo block of a PU, video encoder 20 may generate the predicted videoblock of the PU based on decoded samples of the picture associated withthe PU. If video encoder 20 uses intra prediction to generate predictedvideo blocks of the PUs of a CU, the CU is an intra-predicted CU. Whenvideo encoder 20 uses inter prediction to generate the predicted videoblock of the PU, video encoder 20 may generate the predicted video blockof the PU based on decoded samples of one or more pictures other thanthe picture associated with the PU. If video encoder 20 uses interprediction to generate predicted video blocks of the PUs of a CU, the CUis an inter-predicted CU.

Furthermore, when video encoder 20 uses inter prediction to generate apredicted video block for a PU, video encoder 20 may generate motioninformation for the PU. The motion information for a PU may indicate oneor more reference blocks of the PU. Each reference block of the PU maybe a video block within a reference picture. The reference picture maybe a picture other than the picture associated with the PU. In someinstances, a reference block of a PU may also be referred to as the“reference sample” of the PU. Video encoder 20 may generate thepredicted video block for the PU based on the reference blocks of thePU.

After video encoder 20 generates predicted video blocks for one or morePUs of a CU, video encoder 20 may generate residual data for the CUbased on the predicted video blocks for the PUs of the CU. The residualdata for the CU may indicate differences between samples in thepredicted video blocks for the PUs of the CU and the original videoblock of the CU.

Furthermore, as part of performing an encoding operation on anon-partitioned CU, video encoder 20 may perform recursive quadtreepartitioning on the residual data of the CU to partition the residualdata of the CU into one or more blocks of residual data (e.g., residualvideo blocks) associated with transform units (TUs) of the CU. Each TUof a CU may be associated with a different residual video block.

Video encoder 20 may apply one or more transforms to residual videoblocks associated with the TUs to generate transform coefficient blocks(e.g., blocks of transform coefficients) associated with the TUs.Conceptually, a transform coefficient block may be a two-dimensional(2D) matrix of transform coefficients.

After generating a transform coefficient block, video encoder 20 mayperform a quantization process on the transform coefficient block.Quantization generally refers to a process in which transformcoefficients are quantized to possibly reduce the amount of data used torepresent the transform coefficients, providing further compression. Thequantization process may reduce the bit depth associated with some orall of the transform coefficients. For example, an n-bit transformcoefficient may be rounded down to an m-bit transform coefficient duringquantization, where n is greater than m.

Video encoder 20 may associate each CU with a quantization parameter(QP) value. The QP value associated with a CU may determine how videoencoder 20 quantizes transform coefficient blocks associated with theCU. Video encoder 20 may adjust the degree of quantization applied tothe transform coefficient blocks associated with a CU by adjusting theQP value associated with the CU.

After video encoder 20 quantizes a transform coefficient block, videoencoder 20 may generate sets of syntax elements that represent thetransform coefficients in the quantized transform coefficient block.Video encoder 20 may apply entropy encoding operations, such as ContextAdaptive Binary Arithmetic Coding (CABAC) operations, to some of thesesyntax elements. Other entropy coding techniques such as contentadaptive variable length coding (CAVLC), probability intervalpartitioning entropy (PIPE) coding, or other binary arithmetic codingcould also be used.

The bitstream generated by video encoder 20 may include a series ofNetwork Abstraction Layer (NAL) units. Each of the NAL units may be asyntax structure containing an indication of a type of data in the NALunit and bytes containing the data. For example, a NAL unit may containdata representing a video parameter set, a sequence parameter set, apicture parameter set, a coded slice, supplemental enhancementinformation (SEI), an access unit delimiter, filler data, or anothertype of data. The data in a NAL unit may include various syntaxstructures.

Video decoder 30 may receive the bitstream generated by video encoder20. The bitstream may include a coded representation of the video dataencoded by video encoder 20. When video decoder 30 receives thebitstream, video decoder 30 may perform a parsing operation on thebitstream. When video decoder 30 performs the parsing operation, videodecoder 30 may extract syntax elements from the bitstream. Video decoder30 may reconstruct the pictures of the video data based on the syntaxelements extracted from the bitstream. The process to reconstruct thevideo data based on the syntax elements may be generally reciprocal tothe process performed by video encoder 20 to generate the syntaxelements.

After video decoder 30 extracts the syntax elements associated with aCU, video decoder 30 may generate predicted video blocks for the PUs ofthe CU based on the syntax elements. In addition, video decoder 30 mayinverse quantize transform coefficient blocks associated with TUs of theCU. Video decoder 30 may perform inverse transforms on the transformcoefficient blocks to reconstruct residual video blocks associated withthe TUs of the CU. After generating the predicted video blocks andreconstructing the residual video blocks, video decoder 30 mayreconstruct the video block of the CU based on the predicted videoblocks and the residual video blocks. In this way, video decoder 30 mayreconstruct the video blocks of CUs based on the syntax elements in thebitstream.

Video Encoder

FIG. 2A is a block diagram illustrating an example of a video encoderthat may implement techniques in accordance with aspects described inthis disclosure. Video encoder 20 may be configured to process a singlelayer of a video frame, such as for HEVC. Further, video encoder 20 maybe configured to perform any or all of the techniques of thisdisclosure. As one example, prediction processing unit 100 may beconfigured to perform any or all of the techniques described in thisdisclosure. In another embodiment, the video encoder 20 includes anoptional inter-layer prediction unit 128 that is configured to performany or all of the techniques described in this disclosure. In otherembodiments, inter-layer prediction can be performed by predictionprocessing unit 100 (e.g., inter prediction unit 121 and/or intraprediction unit 126), in which case the inter-layer prediction unit 128may be omitted. However, aspects of this disclosure are not so limited.In some examples, the techniques described in this disclosure may beshared among the various components of video encoder 20. In someexamples, additionally or alternatively, a processor (not shown) may beconfigured to perform any or all of the techniques described in thisdisclosure.

For purposes of explanation, this disclosure describes video encoder 20in the context of HEVC coding. However, the techniques of thisdisclosure may be applicable to other coding standards or methods. Theexample depicted in FIG. 2A is for a single layer codec. However, aswill be described further with respect to FIG. 2B, some or all of thevideo encoder 20 may be duplicated for processing of a multi-layercodec.

Video encoder 20 may perform intra- and inter-coding of video blockswithin video slices. Intra coding relies on spatial prediction to reduceor remove spatial redundancy in video within a given video frame orpicture. Inter-coding relies on temporal prediction to reduce or removetemporal redundancy in video within adjacent frames or pictures of avideo sequence. Intra-mode (I mode) may refer to any of several spatialbased coding modes. Inter-modes, such as uni-directional prediction (Pmode) or bi-directional prediction (B mode), may refer to any of severaltemporal-based coding modes.

In the example of FIG. 2A, video encoder 20 includes a plurality offunctional components. The functional components of video encoder 20include a prediction processing unit 100, a residual generation unit102, a transform processing unit 104, a quantization unit 106, aninverse quantization unit 108, an inverse transform unit 110, areconstruction unit 112, a filter unit 113, a decoded picture buffer114, and an entropy encoding unit 116. Prediction processing unit 100includes an inter prediction unit 121, a motion estimation unit 122, amotion compensation unit 124, an intra prediction unit 126, and aninter-layer prediction unit 128. In other examples, video encoder 20 mayinclude more, fewer, or different functional components. Furthermore,motion estimation unit 122 and motion compensation unit 124 may behighly integrated, but are represented in the example of FIG. 2Aseparately for purposes of explanation.

Video encoder 20 may receive video data. Video encoder 20 may receivethe video data from various sources. For example, video encoder 20 mayreceive the video data from video source 18 (e.g., shown in FIG. 1A or1B) or another source. The video data may represent a series ofpictures. To encode the video data, video encoder 20 may perform anencoding operation on each of the pictures. As part of performing theencoding operation on a picture, video encoder 20 may perform encodingoperations on each slice of the picture. As part of performing anencoding operation on a slice, video encoder 20 may perform encodingoperations on treeblocks in the slice.

As part of performing an encoding operation on a treeblock, predictionprocessing unit 100 may perform quadtree partitioning on the video blockof the treeblock to divide the video block into progressively smallervideo blocks. Each of the smaller video blocks may be associated with adifferent CU. For example, prediction processing unit 100 may partitiona video block of a treeblock into four equally-sized sub-blocks,partition one or more of the sub-blocks into four equally-sizedsub-sub-blocks, and so on.

The sizes of the video blocks associated with CUs may range from 8×8samples up to the size of the treeblock with a maximum of 64×64 samplesor greater. In this disclosure, “N×N” and “N by N” may be usedinterchangeably to refer to the sample dimensions of a video block interms of vertical and horizontal dimensions, e.g., 16×16 samples or 16by 16 samples. In general, a 16×16 video block has sixteen samples in avertical direction (y=16) and sixteen samples in a horizontal direction(x=16). Likewise, an N×N block generally has N samples in a verticaldirection and N samples in a horizontal direction, where N represents anonnegative integer value.

Furthermore, as part of performing the encoding operation on atreeblock, prediction processing unit 100 may generate a hierarchicalquadtree data structure for the treeblock. For example, a treeblock maycorrespond to a root node of the quadtree data structure. If predictionprocessing unit 100 partitions the video block of the treeblock intofour sub-blocks, the root node has four child nodes in the quadtree datastructure. Each of the child nodes corresponds to a CU associated withone of the sub-blocks. If prediction processing unit 100 partitions oneof the sub-blocks into four sub-sub-blocks, the node corresponding tothe CU associated with the sub-block may have four child nodes, each ofwhich corresponds to a CU associated with one of the sub-sub-blocks.

Each node of the quadtree data structure may contain syntax data (e.g.,syntax elements) for the corresponding treeblock or CU. For example, anode in the quadtree may include a split flag that indicates whether thevideo block of the CU corresponding to the node is partitioned (e.g.,split) into four sub-blocks. Syntax elements for a CU may be definedrecursively, and may depend on whether the video block of the CU issplit into sub-blocks. A CU whose video block is not partitioned maycorrespond to a leaf node in the quadtree data structure. A codedtreeblock may include data based on the quadtree data structure for acorresponding treeblock.

Video encoder 20 may perform encoding operations on each non-partitionedCU of a treeblock. When video encoder 20 performs an encoding operationon a non-partitioned CU, video encoder 20 generates data representing anencoded representation of the non-partitioned CU.

As part of performing an encoding operation on a CU, predictionprocessing unit 100 may partition the video block of the CU among one ormore PUs of the CU. Video encoder 20 and video decoder 30 may supportvarious PU sizes. Assuming that the size of a particular CU is 2N×2N,video encoder 20 and video decoder 30 may support PU sizes of 2N×2N orN×N, and inter-prediction in symmetric PU sizes of 2N×2N, 2N×N, N×2N,N×N, 2N×nU, nL×2N, nR×2N, or similar. Video encoder 20 and video decoder30 may also support asymmetric partitioning for PU sizes of 2N×nU,2N×nD, nL×2N, and nR×2N. In some examples, prediction processing unit100 may perform geometric partitioning to partition the video block of aCU among PUs of the CU along a boundary that does not meet the sides ofthe video block of the CU at right angles.

Inter prediction unit 121 may perform inter prediction on each PU of theCU. Inter prediction may provide temporal compression. To perform interprediction on a PU, motion estimation unit 122 may generate motioninformation for the PU. Motion compensation unit 124 may generate apredicted video block for the PU based the motion information anddecoded samples of pictures other than the picture associated with theCU (e.g., reference pictures). In this disclosure, a predicted videoblock generated by motion compensation unit 124 may be referred to as aninter-predicted video block.

Slices may be I slices, P slices, or B slices. Motion estimation unit122 and motion compensation unit 124 may perform different operationsfor a PU of a CU depending on whether the PU is in an I slice, a Pslice, or a B slice. In an I slice, all PUs are intra predicted. Hence,if the PU is in an I slice, motion estimation unit 122 and motioncompensation unit 124 do not perform inter prediction on the PU.

If the PU is in a P slice, the picture containing the PU is associatedwith a list of reference pictures referred to as “list 0.” Each of thereference pictures in list 0 contains samples that may be used for interprediction of other pictures. When motion estimation unit 122 performsthe motion estimation operation with regard to a PU in a P slice, motionestimation unit 122 may search the reference pictures in list 0 for areference block for the PU. The reference block of the PU may be a setof samples, e.g., a block of samples, that most closely corresponds tothe samples in the video block of the PU. Motion estimation unit 122 mayuse a variety of metrics to determine how closely a set of samples in areference picture corresponds to the samples in the video block of a PU.For example, motion estimation unit 122 may determine how closely a setof samples in a reference picture corresponds to the samples in thevideo block of a PU by sum of absolute difference (SAD), sum of squaredifference (SSD), or other difference metrics.

After identifying a reference block of a PU in a P slice, motionestimation unit 122 may generate a reference index that indicates thereference picture in list 0 containing the reference block and a motionvector that indicates a spatial displacement between the PU and thereference block. In various examples, motion estimation unit 122 maygenerate motion vectors to varying degrees of precision. For example,motion estimation unit 122 may generate motion vectors at one-quartersample precision, one-eighth sample precision, or other fractionalsample precision. In the case of fractional sample precision, referenceblock values may be interpolated from integer-position sample values inthe reference picture. Motion estimation unit 122 may output thereference index and the motion vector as the motion information of thePU. Motion compensation unit 124 may generate a predicted video block ofthe PU based on the reference block identified by the motion informationof the PU.

If the PU is in a B slice, the picture containing the PU may beassociated with two lists of reference pictures, referred to as “list 0”and “list 1.” In some examples, a picture containing a B slice may beassociated with a list combination that is a combination of list 0 andlist 1.

Furthermore, if the PU is in a B slice, motion estimation unit 122 mayperform uni-directional prediction or bi-directional prediction for thePU. When motion estimation unit 122 performs uni-directional predictionfor the PU, motion estimation unit 122 may search the reference picturesof list 0 or list 1 for a reference block for the PU. Motion estimationunit 122 may then generate a reference index that indicates thereference picture in list 0 or list 1 that contains the reference blockand a motion vector that indicates a spatial displacement between the PUand the reference block. Motion estimation unit 122 may output thereference index, a prediction direction indicator, and the motion vectoras the motion information of the PU. The prediction direction indicatormay indicate whether the reference index indicates a reference picturein list 0 or list 1. Motion compensation unit 124 may generate thepredicted video block of the PU based on the reference block indicatedby the motion information of the PU.

When motion estimation unit 122 performs bi-directional prediction for aPU, motion estimation unit 122 may search the reference pictures in list0 for a reference block for the PU and may also search the referencepictures in list 1 for another reference block for the PU. Motionestimation unit 122 may then generate reference indexes that indicatethe reference pictures in list 0 and list 1 containing the referenceblocks and motion vectors that indicate spatial displacements betweenthe reference blocks and the PU. Motion estimation unit 122 may outputthe reference indexes and the motion vectors of the PU as the motioninformation of the PU. Motion compensation unit 124 may generate thepredicted video block of the PU based on the reference blocks indicatedby the motion information of the PU.

In some instances, motion estimation unit 122 does not output a full setof motion information for a PU to entropy encoding unit 116. Rather,motion estimation unit 122 may signal the motion information of a PUwith reference to the motion information of another PU. For example,motion estimation unit 122 may determine that the motion information ofthe PU is sufficiently similar to the motion information of aneighboring PU. In this example, motion estimation unit 122 mayindicate, in a syntax structure associated with the PU, a value thatindicates to video decoder 30 that the PU has the same motioninformation as the neighboring PU. In another example, motion estimationunit 122 may identify, in a syntax structure associated with the PU, aneighboring PU and a motion vector difference (MVD). The motion vectordifference indicates a difference between the motion vector of the PUand the motion vector of the indicated neighboring PU. Video decoder 30may use the motion vector of the indicated neighboring PU and the motionvector difference to determine the motion vector of the PU. By referringto the motion information of a first PU when signaling the motioninformation of a second PU, video encoder 20 may be able to signal themotion information of the second PU using fewer bits.

As further discussed below with reference to FIG. 4, the predictionprocessing unit 100 may be configured to code (e.g., encode or decode)the PU (or any other reference layer and/or enhancement layer blocks orvideo units) by performing the methods illustrated in FIG. 4. Forexample, inter prediction unit 121 (e.g., via motion estimation unit 122and/or motion compensation unit 124), intra prediction unit 126, orinter-layer prediction unit 128 may be configured to perform the methodsillustrated in FIG. 4, either together or separately.

As part of performing an encoding operation on a CU, intra predictionunit 126 may perform intra prediction on PUs of the CU. Intra predictionmay provide spatial compression. When intra prediction unit 126 performsintra prediction on a PU, intra prediction unit 126 may generateprediction data for the PU based on decoded samples of other PUs in thesame picture. The prediction data for the PU may include a predictedvideo block and various syntax elements. Intra prediction unit 126 mayperform intra prediction on PUs in I slices, P slices, and B slices.

To perform intra prediction on a PU, intra prediction unit 126 may usemultiple intra prediction modes to generate multiple sets of predictiondata for the PU. When intra prediction unit 126 uses an intra predictionmode to generate a set of prediction data for the PU, intra predictionunit 126 may extend samples from video blocks of neighboring PUs acrossthe video block of the PU in a direction and/or gradient associated withthe intra prediction mode. The neighboring PUs may be above, above andto the right, above and to the left, or to the left of the PU, assuminga left-to-right, top-to-bottom encoding order for PUs, CUs, andtreeblocks. Intra prediction unit 126 may use various numbers of intraprediction modes, e.g., 33 directional intra prediction modes, dependingon the size of the PU.

Prediction processing unit 100 may select the prediction data for a PUfrom among the prediction data generated by motion compensation unit 124for the PU or the prediction data generated by intra prediction unit 126for the PU. In some examples, prediction processing unit 100 selects theprediction data for the PU based on rate/distortion metrics of the setsof prediction data.

If prediction processing unit 100 selects prediction data generated byintra prediction unit 126, prediction processing unit 100 may signal theintra prediction mode that was used to generate the prediction data forthe PUs, e.g., the selected intra prediction mode. Prediction processingunit 100 may signal the selected intra prediction mode in various ways.For example, it may be probable that the selected intra prediction modeis the same as the intra prediction mode of a neighboring PU. In otherwords, the intra prediction mode of the neighboring PU may be the mostprobable mode for the current PU. Thus, prediction processing unit 100may generate a syntax element to indicate that the selected intraprediction mode is the same as the intra prediction mode of theneighboring PU.

As discussed above, the video encoder 20 may include inter-layerprediction unit 128. Inter-layer prediction unit 128 is configured topredict a current block (e.g., a current block in the EL) using one ormore different layers that are available in SVC (e.g., a base orreference layer). Such prediction may be referred to as inter-layerprediction. Inter-layer prediction unit 128 utilizes prediction methodsto reduce inter-layer redundancy, thereby improving coding efficiencyand reducing computational resource requirements. Some examples ofinter-layer prediction include inter-layer intra prediction, inter-layermotion prediction, and inter-layer residual prediction. Inter-layerintra prediction uses the reconstruction of co-located blocks in thebase layer to predict the current block in the enhancement layer.Inter-layer motion prediction uses motion information of the base layerto predict motion in the enhancement layer. Inter-layer residualprediction uses the residue of the base layer to predict the residue ofthe enhancement layer. Each of the inter-layer prediction schemes isdiscussed below in greater detail.

After prediction processing unit 100 selects the prediction data for PUsof a CU, residual generation unit 102 may generate residual data for theCU by subtracting (e.g., indicated by the minus sign) the predictedvideo blocks of the PUs of the CU from the video block of the CU. Theresidual data of a CU may include 2D residual video blocks thatcorrespond to different sample components of the samples in the videoblock of the CU. For example, the residual data may include a residualvideo block that corresponds to differences between luminance componentsof samples in the predicted video blocks of the PUs of the CU andluminance components of samples in the original video block of the CU.In addition, the residual data of the CU may include residual videoblocks that correspond to the differences between chrominance componentsof samples in the predicted video blocks of the PUs of the CU and thechrominance components of the samples in the original video block of theCU.

Prediction processing unit 100 may perform quadtree partitioning topartition the residual video blocks of a CU into sub-blocks. Eachundivided residual video block may be associated with a different TU ofthe CU. The sizes and positions of the residual video blocks associatedwith TUs of a CU may or may not be based on the sizes and positions ofvideo blocks associated with the PUs of the CU. A quadtree structureknown as a “residual quad tree” (RQT) may include nodes associated witheach of the residual video blocks. The TUs of a CU may correspond toleaf nodes of the RQT.

Transform processing unit 104 may generate one or more transformcoefficient blocks for each TU of a CU by applying one or moretransforms to a residual video block associated with the TU. Each of thetransform coefficient blocks may be a 2D matrix of transformcoefficients. Transform processing unit 104 may apply various transformsto the residual video block associated with a TU. For example, transformprocessing unit 104 may apply a discrete cosine transform (DCT), adirectional transform, or a conceptually similar transform to theresidual video block associated with a TU.

After transform processing unit 104 generates a transform coefficientblock associated with a TU, quantization unit 106 may quantize thetransform coefficients in the transform coefficient block. Quantizationunit 106 may quantize a transform coefficient block associated with a TUof a CU based on a QP value associated with the CU.

Video encoder 20 may associate a QP value with a CU in various ways. Forexample, video encoder 20 may perform a rate-distortion analysis on atreeblock associated with the CU. In the rate-distortion analysis, videoencoder 20 may generate multiple coded representations of the treeblockby performing an encoding operation multiple times on the treeblock.Video encoder 20 may associate different QP values with the CU whenvideo encoder 20 generates different encoded representations of thetreeblock. Video encoder 20 may signal that a given QP value isassociated with the CU when the given QP value is associated with the CUin a coded representation of the treeblock that has a lowest bitrate anddistortion metric.

Inverse quantization unit 108 and inverse transform unit 110 may applyinverse quantization and inverse transforms to the transform coefficientblock, respectively, to reconstruct a residual video block from thetransform coefficient block. Reconstruction unit 112 may add thereconstructed residual video block to corresponding samples from one ormore predicted video blocks generated by prediction processing unit 100to produce a reconstructed video block associated with a TU. Byreconstructing video blocks for each TU of a CU in this way, videoencoder 20 may reconstruct the video block of the CU.

After reconstruction unit 112 reconstructs the video block of a CU,filter unit 113 may perform a deblocking operation to reduce blockingartifacts in the video block associated with the CU. After performingthe one or more deblocking operations, filter unit 113 may store thereconstructed video block of the CU in decoded picture buffer 114.Motion estimation unit 122 and motion compensation unit 124 may use areference picture that contains the reconstructed video block to performinter prediction on PUs of subsequent pictures. In addition, intraprediction unit 126 may use reconstructed video blocks in decodedpicture buffer 114 to perform intra prediction on other PUs in the samepicture as the CU.

Entropy encoding unit 116 may receive data from other functionalcomponents of video encoder 20. For example, entropy encoding unit 116may receive transform coefficient blocks from quantization unit 106 andmay receive syntax elements from prediction processing unit 100. Whenentropy encoding unit 116 receives the data, entropy encoding unit 116may perform one or more entropy encoding operations to generate entropyencoded data. For example, video encoder 20 may perform a contextadaptive variable length coding (CAVLC) operation, a CABAC operation, avariable-to-variable (V2V) length coding operation, a syntax-basedcontext-adaptive binary arithmetic coding (SBAC) operation, aProbability Interval Partitioning Entropy (PIPE) coding operation, oranother type of entropy encoding operation on the data. Entropy encodingunit 116 may output a bitstream that includes the entropy encoded data.

As part of performing an entropy encoding operation on data, entropyencoding unit 116 may select a context model. If entropy encoding unit116 is performing a CABAC operation, the context model may indicateestimates of probabilities of particular bins having particular values.In the context of CABAC, the term “bin” is used to refer to a bit of abinarized version of a syntax element.

Multi-Layer Video Encoder

FIG. 2B is a block diagram illustrating an example of a multi-layervideo encoder 23 that may implement techniques in accordance withaspects described in this disclosure. The video encoder 23 may beconfigured to process multi-layer video frames, such as for SHVC andmultiview coding. Further, the video encoder 23 may be configured toperform any or all of the techniques of this disclosure.

The video encoder 23 includes a video encoder 20A and video encoder 20B,each of which may be configured as the video encoder 20 and may performthe functions described above with respect to the video encoder 20.Further, as indicated by the reuse of reference numbers, the videoencoders 20A and 20B may include at least some of the systems andsubsystems as the video encoder 20. Although the video encoder 23 isillustrated as including two video encoders 20A and 20B, the videoencoder 23 is not limited as such and may include any number of videoencoder 20 layers. In some embodiments, the video encoder 23 may includea video encoder 20 for each picture or frame in an access unit. Forexample, an access unit that includes five pictures may be processed orencoded by a video encoder that includes five encoder layers. In someembodiments, the video encoder 23 may include more encoder layers thanframes in an access unit. In some such cases, some of the video encoderlayers may be inactive when processing some access units.

In addition to the video encoders 20A and 20B, the video encoder 23 mayinclude an resampling unit 90. The resampling unit 90 may, in somecases, upsample a base layer of a received video frame to, for example,create an enhancement layer. The resampling unit 90 may upsampleparticular information associated with the received base layer of aframe, but not other information. For example, the resampling unit 90may upsample the spatial size or number of pixels of the base layer, butthe number of slices or the picture order count may remain constant. Insome cases, the resampling unit 90 may not process the received videoand/or may be optional. For example, in some cases, the predictionprocessing unit 100 may perform upsampling. In some embodiments, theresampling unit 90 is configured to upsample a layer and reorganize,redefine, modify, or adjust one or more slices to comply with a set ofslice boundary rules and/or raster scan rules. Although primarilydescribed as upsampling a base layer, or a lower layer in an accessunit, in some cases, the resampling unit 90 may downsample a layer. Forexample, if during streaming of a video bandwidth is reduced, a framemay be downsampled instead of upsampled.

The resampling unit 90 may be configured to receive a picture or frame(or picture information associated with the picture) from the decodedpicture buffer 114 of the lower layer encoder (e.g., the video encoder20A) and to upsample the picture (or the received picture information).This upsampled picture may then be provided to the prediction processingunit 100 of a higher layer encoder (e.g., the video encoder 20B)configured to encode a picture in the same access unit as the lowerlayer encoder. In some cases, the higher layer encoder is one layerremoved from the lower layer encoder. In other cases, there may be oneor more higher layer encoders between the layer 0 video encoder and thelayer 1 encoder of FIG. 2B.

In some cases, the resampling unit 90 may be omitted or bypassed. Insuch cases, the picture from the decoded picture buffer 114 of the videoencoder 20A may be provided directly, or at least without being providedto the resampling unit 90, to the prediction processing unit 100 of thevideo encoder 20B. For example, if video data provided to the videoencoder 20B and the reference picture from the decoded picture buffer114 of the video encoder 20A are of the same size or resolution, thereference picture may be provided to the video encoder 20B without anyresampling.

In some embodiments, the video encoder 23 downsamples video data to beprovided to the lower layer encoder using the downsampling unit 94before provided the video data to the video encoder 20A. Alternatively,the downsampling unit 94 may be a resampling unit 90 capable ofupsampling or downsampling the video data. In yet other embodiments, thedownsampling unit 94 may be omitted.

As illustrated in FIG. 2B, the video encoder 23 may further include amultiplexor 98, or mux. The mux 98 can output a combined bitstream fromthe video encoder 23. The combined bitstream may be created by taking abitstream from each of the video encoders 20A and 20B and alternatingwhich bitstream is output at a given time. While in some cases the bitsfrom the two (or more in the case of more than two video encoder layers)bitstreams may be alternated one bit at a time, in many cases thebitstreams are combined differently. For example, the output bitstreammay be created by alternating the selected bitstream one block at atime. In another example, the output bitstream may be created byoutputting a non-1:1 ratio of blocks from each of the video encoders 20Aand 20B. For instance, two blocks may be output from the video encoder20B for each block output from the video encoder 20A. In someembodiments, the output stream from the mux 98 may be preprogrammed. Inother embodiments, the mux 98 may combine the bitstreams from the videoencoders 20A, 20B based on a control signal received from a systemexternal to the video encoder 23, such as from a processor on a sourcedevice including the source module 12. The control signal may begenerated based on the resolution or bitrate of a video from the videosource 18, based on a bandwidth of the link 16, based on a subscriptionassociated with a user (e.g., a paid subscription versus a freesubscription), or based on any other factor for determining a resolutionoutput desired from the video encoder 23.

Video Decoder

FIG. 3A is a block diagram illustrating an example of a video decoderthat may implement techniques in accordance with aspects described inthis disclosure. The video decoder 30 may be configured to process asingle layer of a video frame, such as for HEVC. Further, video decoder30 may be configured to perform any or all of the techniques of thisdisclosure. As one example, motion compensation unit 162 and/or intraprediction unit 164 may be configured to perform any or all of thetechniques described in this disclosure. In one embodiment, videodecoder 30 may optionally include inter-layer prediction unit 166 thatis configured to perform any or all of the techniques described in thisdisclosure. In other embodiments, inter-layer prediction can beperformed by prediction processing unit 152 (e.g., motion compensationunit 162 and/or intra prediction unit 164), in which case theinter-layer prediction unit 166 may be omitted. However, aspects of thisdisclosure are not so limited. In some examples, the techniquesdescribed in this disclosure may be shared among the various componentsof video decoder 30. In some examples, additionally or alternatively, aprocessor (not shown) may be configured to perform any or all of thetechniques described in this disclosure.

For purposes of explanation, this disclosure describes video decoder 30in the context of HEVC coding. However, the techniques of thisdisclosure may be applicable to other coding standards or methods. Theexample depicted in FIG. 3A is for a single layer codec. However, aswill be described further with respect to FIG. 3B, some or all of thevideo decoder 30 may be duplicated for processing of a multi-layercodec.

In the example of FIG. 3A, video decoder 30 includes a plurality offunctional components. The functional components of video decoder 30include an entropy decoding unit 150, a prediction processing unit 152,an inverse quantization unit 154, an inverse transform unit 156, areconstruction unit 158, a filter unit 159, and a decoded picture buffer160. Prediction processing unit 152 includes a motion compensation unit162, an intra prediction unit 164, and an inter-layer prediction unit166. In some examples, video decoder 30 may perform a decoding passgenerally reciprocal to the encoding pass described with respect tovideo encoder 20 of FIG. 2A. In other examples, video decoder 30 mayinclude more, fewer, or different functional components.

Video decoder 30 may receive a bitstream that comprises encoded videodata. The bitstream may include a plurality of syntax elements. Whenvideo decoder 30 receives the bitstream, entropy decoding unit 150 mayperform a parsing operation on the bitstream. As a result of performingthe parsing operation on the bitstream, entropy decoding unit 150 mayextract syntax elements from the bitstream. As part of performing theparsing operation, entropy decoding unit 150 may entropy decode entropyencoded syntax elements in the bitstream. Prediction processing unit152, inverse quantization unit 154, inverse transform unit 156,reconstruction unit 158, and filter unit 159 may perform areconstruction operation that generates decoded video data based on thesyntax elements extracted from the bitstream.

As discussed above, the bitstream may comprise a series of NAL units.The NAL units of the bitstream may include video parameter set NALunits, sequence parameter set NAL units, picture parameter set NALunits, SEI NAL units, and so on. As part of performing the parsingoperation on the bitstream, entropy decoding unit 150 may performparsing operations that extract and entropy decode sequence parametersets from sequence parameter set NAL units, picture parameter sets frompicture parameter set NAL units, SEI data from SEI NAL units, and so on.

In addition, the NAL units of the bitstream may include coded slice NALunits. As part of performing the parsing operation on the bitstream,entropy decoding unit 150 may perform parsing operations that extractand entropy decode coded slices from the coded slice NAL units. Each ofthe coded slices may include a slice header and slice data. The sliceheader may contain syntax elements pertaining to a slice. The syntaxelements in the slice header may include a syntax element thatidentifies a picture parameter set associated with a picture thatcontains the slice. Entropy decoding unit 150 may perform entropydecoding operations, such as CABAC decoding operations, on syntaxelements in the coded slice header to recover the slice header.

As part of extracting the slice data from coded slice NAL units, entropydecoding unit 150 may perform parsing operations that extract syntaxelements from coded CUs in the slice data. The extracted syntax elementsmay include syntax elements associated with transform coefficientblocks. Entropy decoding unit 150 may then perform CABAC decodingoperations on some of the syntax elements.

After entropy decoding unit 150 performs a parsing operation on anon-partitioned CU, video decoder 30 may perform a reconstructionoperation on the non-partitioned CU. To perform the reconstructionoperation on a non-partitioned CU, video decoder 30 may perform areconstruction operation on each TU of the CU. By performing thereconstruction operation for each TU of the CU, video decoder 30 mayreconstruct a residual video block associated with the CU.

As part of performing a reconstruction operation on a TU, inversequantization unit 154 may inverse quantize, e.g., de-quantize, atransform coefficient block associated with the TU. Inverse quantizationunit 154 may inverse quantize the transform coefficient block in amanner similar to the inverse quantization processes proposed for HEVCor defined by the H.264 decoding standard. Inverse quantization unit 154may use a quantization parameter QP calculated by video encoder 20 for aCU of the transform coefficient block to determine a degree ofquantization and, likewise, a degree of inverse quantization for inversequantization unit 154 to apply.

After inverse quantization unit 154 inverse quantizes a transformcoefficient block, inverse transform unit 156 may generate a residualvideo block for the TU associated with the transform coefficient block.Inverse transform unit 156 may apply an inverse transform to thetransform coefficient block in order to generate the residual videoblock for the TU. For example, inverse transform unit 156 may apply aninverse DCT, an inverse integer transform, an inverse Karhunen-Loevetransform (KLT), an inverse rotational transform, an inverse directionaltransform, or another inverse transform to the transform coefficientblock. In some examples, inverse transform unit 156 may determine aninverse transform to apply to the transform coefficient block based onsignaling from video encoder 20. In such examples, inverse transformunit 156 may determine the inverse transform based on a signaledtransform at the root node of a quadtree for a treeblock associated withthe transform coefficient block. In other examples, inverse transformunit 156 may infer the inverse transform from one or more codingcharacteristics, such as block size, coding mode, or the like. In someexamples, inverse transform unit 156 may apply a cascaded inversetransform.

In some examples, motion compensation unit 162 may refine the predictedvideo block of a PU by performing interpolation based on interpolationfilters. Identifiers for interpolation filters to be used for motioncompensation with sub-sample precision may be included in the syntaxelements. Motion compensation unit 162 may use the same interpolationfilters used by video encoder 20 during generation of the predictedvideo block of the PU to calculate interpolated values for sub-integersamples of a reference block. Motion compensation unit 162 may determinethe interpolation filters used by video encoder 20 according to receivedsyntax information and use the interpolation filters to produce thepredicted video block.

As further discussed below with reference to FIG. 4, the predictionprocessing unit 152 may code (e.g., encode or decode) the PU (or anyother reference layer and/or enhancement layer blocks or video units) byperforming the methods illustrated in FIG. 4. For example, motioncompensation unit 162, intra prediction unit 164, or inter-layerprediction unit 166 may be configured to perform the methods illustratedin FIG. 4, either together or separately.

If a PU is encoded using intra prediction, intra prediction unit 164 mayperform intra prediction to generate a predicted video block for the PU.For example, intra prediction unit 164 may determine an intra predictionmode for the PU based on syntax elements in the bitstream. The bitstreammay include syntax elements that intra prediction unit 164 may use todetermine the intra prediction mode of the PU.

In some instances, the syntax elements may indicate that intraprediction unit 164 is to use the intra prediction mode of another PU todetermine the intra prediction mode of the current PU. For example, itmay be probable that the intra prediction mode of the current PU is thesame as the intra prediction mode of a neighboring PU. In other words,the intra prediction mode of the neighboring PU may be the most probablemode for the current PU. Hence, in this example, the bitstream mayinclude a small syntax element that indicates that the intra predictionmode of the PU is the same as the intra prediction mode of theneighboring PU. Intra prediction unit 164 may then use the intraprediction mode to generate prediction data (e.g., predicted samples)for the PU based on the video blocks of spatially neighboring PUs.

As discussed above, video decoder 30 may also include inter-layerprediction unit 166. Inter-layer prediction unit 166 is configured topredict a current block (e.g., a current block in the EL) using one ormore different layers that are available in SVC (e.g., a base orreference layer). Such prediction may be referred to as inter-layerprediction. Inter-layer prediction unit 166 utilizes prediction methodsto reduce inter-layer redundancy, thereby improving coding efficiencyand reducing computational resource requirements. Some examples ofinter-layer prediction include inter-layer intra prediction, inter-layermotion prediction, and inter-layer residual prediction. Inter-layerintra prediction uses the reconstruction of co-located blocks in thebase layer to predict the current block in the enhancement layer.Inter-layer motion prediction uses motion information of the base layerto predict motion in the enhancement layer. Inter-layer residualprediction uses the residue of the base layer to predict the residue ofthe enhancement layer. Each of the inter-layer prediction schemes isdiscussed below in greater detail.

Reconstruction unit 158 may use the residual video blocks associatedwith TUs of a CU and the predicted video blocks of the PUs of the CU,e.g., either intra-prediction data or inter-prediction data, asapplicable, to reconstruct the video block of the CU. Thus, videodecoder 30 may generate a predicted video block and a residual videoblock based on syntax elements in the bitstream and may generate a videoblock based on the predicted video block and the residual video block.

After reconstruction unit 158 reconstructs the video block of the CU,filter unit 159 may perform a deblocking operation to reduce blockingartifacts associated with the CU. After filter unit 159 performs adeblocking operation to reduce blocking artifacts associated with theCU, video decoder 30 may store the video block of the CU in decodedpicture buffer 160. Decoded picture buffer 160 may provide referencepictures for subsequent motion compensation, intra prediction, andpresentation on a display device, such as display device 32 of FIG. 1Aor 1B. For instance, video decoder 30 may perform, based on the videoblocks in decoded picture buffer 160, intra prediction or interprediction operations on PUs of other CUs.

Multi-Layer Decoder

FIG. 3B is a block diagram illustrating an example of a multi-layervideo decoder 33 that may implement techniques in accordance withaspects described in this disclosure. The video decoder 33 may beconfigured to process multi-layer video frames, such as for SHVC andmultiview coding. Further, the video decoder 33 may be configured toperform any or all of the techniques of this disclosure.

The video decoder 33 includes a video decoder 30A and video decoder 30B,each of which may be configured as the video decoder 30 and may performthe functions described above with respect to the video decoder 30.Further, as indicated by the reuse of reference numbers, the videodecoders 30A and 30B may include at least some of the systems andsubsystems as the video decoder 30. Although the video decoder 33 isillustrated as including two video decoders 30A and 30B, the videodecoder 33 is not limited as such and may include any number of videodecoder 30 layers. In some embodiments, the video decoder 33 may includea video decoder 30 for each picture or frame in an access unit. Forexample, an access unit that includes five pictures may be processed ordecoded by a video decoder that includes five decoder layers. In someembodiments, the video decoder 33 may include more decoder layers thanframes in an access unit. In some such cases, some of the video decoderlayers may be inactive when processing some access units.

In addition to the video decoders 30A and 30B, the video decoder 33 mayinclude an upsampling unit 92. In some embodiments, the upsampling unit92 may upsample a base layer of a received video frame to create anenhanced layer to be added to the reference picture list for the frameor access unit. This enhanced layer can be stored in the decoded picturebuffer 160. In some embodiments, the upsampling unit 92 can include someor all of the embodiments described with respect to the resampling unit90 of FIG. 2A. In some embodiments, the upsampling unit 92 is configuredto upsample a layer and reorganize, redefine, modify, or adjust one ormore slices to comply with a set of slice boundary rules and/or rasterscan rules. In some cases, the upsampling unit 92 may be a resamplingunit configured to upsample and/or downsample a layer of a receivedvideo frame

The upsampling unit 92 may be configured to receive a picture or frame(or picture information associated with the picture) from the decodedpicture buffer 160 of the lower layer decoder (e.g., the video decoder30A) and to upsample the picture (or the received picture information).This upsampled picture may then be provided to the prediction processingunit 152 of a higher layer decoder (e.g., the video decoder 30B)configured to decode a picture in the same access unit as the lowerlayer decoder. In some cases, the higher layer decoder is one layerremoved from the lower layer decoder. In other cases, there may be oneor more higher layer decoders between the layer 0 decoder and the layer1 decoder of FIG. 3B.

In some cases, the upsampling unit 92 may be omitted or bypassed. Insuch cases, the picture from the decoded picture buffer 160 of the videodecoder 30A may be provided directly, or at least without being providedto the upsampling unit 92, to the prediction processing unit 152 of thevideo decoder 30B. For example, if video data provided to the videodecoder 30B and the reference picture from the decoded picture buffer160 of the video decoder 30A are of the same size or resolution, thereference picture may be provided to the video decoder 30B withoutupsampling. Further, in some embodiments, the upsampling unit 92 may bea resampling unit 90 configured to upsample or downsample a referencepicture received from the decoded picture buffer 160 of the videodecoder 30A.

As illustrated in FIG. 3B, the video decoder 33 may further include ademultiplexor 99, or demux. The demux 99 can split an encoded videobitstream into multiple bitstreams with each bitstream output by thedemux 99 being provided to a different video decoder 30A and 30B. Themultiple bitstreams may be created by receiving a bitstream and each ofthe video decoders 30A and 30B receives a portion of the bitstream at agiven time. While in some cases the bits from the bitstream received atthe demux 99 may be alternated one bit at a time between each of thevideo decoders (e.g., video decoders 30A and 30B in the example of FIG.3B), in many cases the bitstream is divided differently. For example,the bitstream may be divided by alternating which video decoder receivesthe bitstream one block at a time. In another example, the bitstream maybe divided by a non-1:1 ratio of blocks to each of the video decoders30A and 30B. For instance, two blocks may be provided to the videodecoder 30B for each block provided to the video decoder 30A. In someembodiments, the division of the bitstream by the demux 99 may bepreprogrammed. In other embodiments, the demux 99 may divide thebitstream based on a control signal received from a system external tothe video decoder 33, such as from a processor on a destination deviceincluding the destination module 14. The control signal may be generatedbased on the resolution or bitrate of a video from the input interface28, based on a bandwidth of the link 16, based on a subscriptionassociated with a user (e.g., a paid subscription versus a freesubscription), or based on any other factor for determining a resolutionobtainable by the video decoder 33.

Intra Random Access Point (IRAP) Pictures

Some video coding schemes may provide various random access pointsthroughout the bitstream such that the bitstream may be decoded startingfrom any of those random access points without needing to decode anypictures that precede those random access points in the bitstream. Insuch video coding schemes, all pictures that follow a random accesspoint in output order (e.g., including those pictures that are in thesame access unit as the picture providing the random access point) canbe correctly decoded without using any pictures that precede the randomaccess point. For example, even if a portion of the bitstream is lostduring transmission or during decoding, a decoder can resume decodingthe bitstream starting from the next random access point. Support forrandom access may facilitate, for example, dynamic streaming services,seek operations, channel switching, etc.

In some coding schemes, such random access points may be provided bypictures that are referred to as intra random access point (IRAP)pictures. For example, a random access point (e.g., provided by anenhancement layer IRAP picture) in an enhancement layer (“layerA”)contained in an access unit (“auA”) may provide layer-specific randomaccess such that for each reference layer (“layerB”) of layerA (e.g., areference layer being a layer that is used to predict layerA) having arandom access point contained in an access unit (“auB”) that is inlayerB and precedes auA in decoding order (or a random access pointcontained in auA), the pictures in layerA that follow auB in outputorder (including those pictures located in auB), are correctly decodablewithout needing to decode any pictures in layerA that precede auB.

IRAP pictures may be coded using intra prediction (e.g., coded withoutreferring to other pictures) or inter-layer prediction, and may include,for example, instantaneous decoder refresh (IDR) pictures, clean randomaccess (CRA) pictures, and broken link access (BLA) pictures. When thereis an IDR picture in the bitstream, all the pictures that precede theIDR picture in decoding order are not used for prediction by picturesthat follow the IDR picture. When there is a CRA picture in thebitstream, the pictures that follow the CRA picture may or may not usepictures that precede the CRA picture in decoding order for prediction.Those pictures that follow the CRA picture in decoding order but usepictures that precede the CRA picture in decoding order may be referredto as random access skipped leading (RASL) pictures. Another type ofpicture that can follow an IRAP picture in decoding order and precede itin output order is a random access decodable leading (RADL) picture,which may not contain references to any pictures that precede the IRAPpicture in decoding order. RASL pictures may be discarded by the decoderif the pictures that precede the CRA picture are not available. A BLApicture indicates to the decoder that pictures that precede the BLApicture may not be available to the decoder (e.g., because twobitstreams are spliced together and the BLA picture is the first pictureof the second bitstream in decoding order). An access unit (e.g., agroup of pictures consisting of all the coded pictures associated withthe same output time across multiple layers) containing a base layerpicture (e.g., having a layer ID value of “0”) that is an IRAP picturemay be referred to as an IRAP access unit.

Network Abstraction Layer (NAL) Units and Parameter Sets

As discussed above, the parameters used by an encoder or a decoder maybe grouped into parameter sets based on the coding level in which theymay be utilized. For example, parameters that are utilized by one ormore coded video sequences in the bitstream may be included in a videoparameter set (VPS), and parameters that are utilized by one or morepictures in a coded video sequence may be included in a sequenceparameter set (SPS). Similarly, parameters that are utilized by one ormore slices in a picture may be included in a picture parameter set(PPS), and other parameters that are specific to a single slice may beincluded in a slice header. Similarly, the indication of which parameterset(s) a particular layer is using (e.g., active) at a given time may beprovided at various coding levels. For example, if the slice header of aslice in the particular layer refers to a PPS, the PPS is activated forthe slice or the picture containing the slice. Similarly, if the PPSrefers to an SPS, the SPS is activated for the picture or the codedvideo sequence containing the picture, and if the SPS refers to a VPS,the VPS is activated for the coded video sequence or the video layercontaining the coded video sequence.

Such parameter sets may be provided in a bitstream in the form ofparameter set NAL units (e.g., SPS NAL unit, PPS NAL unit, etc.). A NALunit may comprise a raw byte sequence payload (RBSP) and a NAL unitheader. The RBSP may specify a parameter set ID (e.g., SPS ID), and theNAL unit header may specify the layer ID, which may indicate whichlayers may use the SPS.

Activation of Sequence Parameter Set (SPS) Raw Byte Sequence Payload(RBSP)

An SPS RBSP includes parameters that can be referred to by one or morepicture parameter set (PPS) RBSPs or one or more SEI NAL unitscontaining an active parameter sets SEI message. Each SPS RBSP mayinitially be considered to be not active for any layer at the start ofthe decoding process. For each layer, at most one SPS RBSP is consideredto be active at any given moment during the decoding process, and theactivation of any particular SPS RBSP for a particular layer results inthe deactivation of the previously-active SPS RBSP for that particularlayer, if any.

One SPS RBSP may be the active SPS RBSP for more than one layer. Forexample, if a base layer and an enhancement layer both contain a picturethat refers to a PPS that in turn refers to an SPS having an SPS ID of3, the SPS having an SPS ID of 3 is the active SPS RBSP for both thereference layer and the enhancement layer.

When an SPS RBSP (e.g., having a particular SPS ID) is not alreadyactive for a particular non-base layer (e.g., having a non-zero layer IDvalue or a layer ID greater than 0) having a layer ID (e.g.,nuh_layer_id) of X, and the SPS RBSP is referred to by activation of apicture parameter set (PPS) RBSP (e.g., in which the PPS ID is equal tothe particular SPS ID of the SPS RBSP), the SPS RBSP is activated forthe particular non-base layer. This SPS may be referred to as the activeSPS RBSP for the particular non-base layer until it is deactivated bythe activation of another SPS RBSP for the particular non-base layer.

Layer Initialization Picture (LIP)

In some coding schemes, a layer initialization picture (“LIP picture”)may be defined as a picture that is an IRAP picture that has aNoRaslOutputFlag flag (e.g., a flag that indicates that RASL picturesare not to be output if the value is set to “1” and indicates that RASLpictures are to be output if the value is set to “0”) set to a value of“1” or a picture that is contained an initial IRAP access unit, which isan IRAP access unit in which the base layer picture (e.g., a picturehaving a layer ID value of “0” or smallest layer ID defined in thebitstream) has the NoRaslOutputFlag set to a value of “1”.

In some embodiments, an SPS can be activated at each LIP picture. Forexample, each IRAP picture that has a NoRaslOutputFlag flag set to avalue of “1” or each picture that is contained in an initial IRAP accessunit, a new SPS, which may be different (e.g., specifying differentpicture resolutions, etc.) from the SPS that was previously activated.However, in a case where the LIP picture is not an IRAP picture (e.g.,any picture contained in an initial IRAP access unit) and the base layerpicture in the initial IRAP access unit is an IDR picture with a flagNoClrasOutputFlag flag (e.g., a flag that indicates that cross-layerrandom access skip pictures are not to be output if the value is set to“1” and indicates that cross-layer random access skip pictures are to beoutput if the value is set to “0”) set to a value of “0”, the LIPpicture should not be allowed to activate a new SPS. If a new SPS isactivated at such the LIP picture in such a case, particularly when thecontents of the SPS RBSP of the new SPS is different from that of theSPS that was previously active prior to the initial IRAP access unit,there could be problems in differing picture resolutions and errorresilience. For example, the new SPS may update the resolution and usetemporal prediction to refer to pictures of different sizes.

In some embodiments, NoClRasOutputFlag and NoRaslOutputFlag may bevariables derived based on the information included in the bitstream.For example, NoRaslOutputFlag may be derived for every IRAP picture(e.g., in BL and/or EL), and NoClRasOutputFlag may be derived only forthe lowest layer pictures (e.g., BL pictures). The value of each ofNoClRasOutputFlag and NoRaslOutputFlag may indicate that some picturesin the bitstream may not be correctly decodable due to theunavailability of certain reference pictures. Such unavailability ofreference pictures may occur at random access points. Cross-layer randomaccess skip (CL-RAS) pictures are, in some ways, the multi-layerequivalent of RASL pictures. If a decoder starts decoding a bitstream ata random access point (e.g., an access unit having a BL IRAP picture),and the EL picture in the access unit is not an IRAP picture, then thatEL picture is a CL-RAS picture. All pictures in the EL may be CL-RASpictures (e.g., decodable, but not correctly decodable) until an IRAPpicture occurs in the EL. When such an EL IRAP picture is provided inthe bitstream, the EL may be said to have been initialized.

Duration of Active SPS RBSP

In order to prevent activation of a new SPS by a LIP picture that is anon-IRAP picture other than at a splice point, which may cause theproblems described above, the activated SPS RBSP may be forced to remainactive for a certain period of time. In some embodiments, an activatedSPS RBSP for a particular layer is to remain active for the entire codedlayer-wise video sequence (CLVS) of that particular layer. A CLVS mayrefer to a sequence of coded pictures, which are in the same layer(e.g., having the same layer ID value), that consists, in decodingorder, of an IRAP picture with NoRaslOutputFlag equal to a value of “1”or a picture with FirstPicInLayerDecodedFlag equal to a value of “0”(e.g., indicating that the picture is the first picture in the layer),followed by all coded pictures, if any, up to but excluding the nextIRAP picture with NoRaslOutputFlag equal to a value of “1” or the nextpicture with FirstPicInLayerDecodedFlag equal to a value of “0”.

In some embodiments, an activated SPS RBSP for a particular layer is toremain active for a sequence of pictures in decoding order in theparticular layer as follows: (1) If the particular nuh_layer_id value isequal to 0, the activated SPS shall remain active for the entire CVS;and (2) otherwise (e.g., the layer ID of the particular layer is notequal to 0), the activated SPS is to remain active starting from an LIPpicture that is an IRAP picture in the particular layer, or an LIPpicture that is not an IRAP picture and that is contained in an IRAPaccess unit containing a base layer picture that is an IRAP picture andhas a NoClrasOutputFlag value of “1”, until the next LIP picture that isan IRAP picture in the particular layer, or an initial IRAP access unitcontaining a base layer picture that is an IRAP picture and has aNoClrasOutputFlag value of “1”.

Bitstream Including a Splice Point

With reference to FIG. 4, an example bitstream having a splice pointwill be described. FIG. 4 shows a multi-layer bitstream 400 created bysplicing bitstreams 410 and 420. The bitstream 410 includes anenhancement layer (EL) 410A and a base layer (BL) 410B, and thebitstream 420 includes an EL 420A and a BL 420B. The EL 410A includes anEL picture 412A, and the BL 410B includes a BL picture 412B. The EL 420Aincludes EL pictures 422A, 424A, and 426A, and the BL 420B includes BLpictures 422B, 424B, and 426B. The multi-layer bitstream 400 furtherincludes access units (AUs) 430-460. The AU 430 includes the EL picture412A and the BL picture 412B, the AU 440 includes the EL picture 422Aand the BL picture 422B, the AU 450 includes the EL picture 424A and theBL picture 424B, and the AU 460 includes the EL picture 426A and the BLpicture 426B. In the example of FIG. 4, the BL picture 422B is an IRAPpicture, and the corresponding EL picture 422A in the AU 440 is atrailing picture (e.g., a non-IRAP picture), and consequently, the AU440 is a non-aligned IRAP AU. Also, it should be noted that the AU 440is an access unit that immediately follows a splice point 470.

Although the example of FIG. 4 illustrates a case where two differentbitstreams are joined together, in some embodiments, a splice point maybe present when a portion of the bitstream is removed. For example, abitstream may have portions A, B, and C, portion B being betweenportions A and C. If portion B is removed from the bitstream, theremaining portions A and C may be joined together, and the point atwhich they are joined together may be referred to as a splice point.More generally, a splice point as discussed in the present applicationmay be deemed to be present when one or more signaled or derivedparameters or flags have predetermined values. For example, withoutreceiving a specific indication that a splice point exists at aparticular location, a decoder may determine the value of a flag (e.g.,NoClrasOutputFlag), and perform one or more techniques described in thisapplication based on the value of the flag.

Restricting Activation of New Parameter Set

FIG. 5 is a flowchart illustrating a method 500 for coding videoinformation, according to an embodiment of the present disclosure. Thesteps illustrated in FIG. 5 may be performed by an encoder (e.g., thevideo encoder as shown in FIG. 2A or FIG. 2B), a decoder (e.g., thevideo decoder as shown in FIG. 3A or FIG. 3B), or any other component.For convenience, method 500 is described as performed by a coder, whichmay be the encoder, the decoder, or another component.

The method 500 begins at block 501. At block 505, the coder determineswhether an enhancement layer (EL) picture is an IRAP picture. Forexample, if the EL picture is any of an IDR picture, a CRA picture, or aBLA picture, the coder may determine the EL picture to be an IRAPpicture. In some embodiments, the coder determines that the EL pictureis an IRAP picture by checking the NAL unit type associated with the ELpicture. If the coder determines that the EL picture is an IRAP picture,the method 500 proceeds to block 520. If the coder determines that theEL picture is not an IRAP picture, the process 500 proceeds to block510.

At block 510, the coder determines whether the EL picture is at a splicepoint. A splice point may indicate the point at which two bitstreams arejoined. For example, the last picture of a first bitstream may beimmediately followed, in coding order, by the first picture of a secondbitstream. In some embodiments, the coder may determine whether the ELpicture is at a splice point by determining whether the EL picture isthe first picture that follows the splice point in coding order. If thecoder determines that the EL picture is at a splice point, the method500 proceeds to block 520. If the coder determines that the EL pictureis not at a splice point, the method 500 proceeds to block 515. Asdiscussed above with reference to FIG. 4, the determination in 510 maycomprise determining whether one or more signaled or derived parametersor flags have predetermined values. For example, without receiving aspecific indication that a splice point exists at a particular location,an encoder or a decoder may determine the value of a flag (e.g.,NoClrasOutputFlag), and proceed to either block 515 or block 520 basedon the determination.

At block 515, the coder disallows activation of a new parameter set. Forexample, the coder may prevent the EL picture from activating a new SPS.The coder may disallow activation of a new parameter set by causing thepreviously activated parameter set to remain active until the next IRAPpicture in the EL is processed. Alternatively, the coder may disallowactivation of a new parameter set by causing the previously activatedparameter set to remain active until the next splice point. In yetanother example, the coder may disallow activation of a new parameterset by causing the previously activated parameter set to remain activeuntil the end of the coded video sequence containing the EL picture.

At block 520, the coder allows activation of a new parameter set. Forexample, the coder may cause the enhancement layer to be associated witha new parameter set that has different parameters than the parameter setthat was previously activated for the EL. The method 500 ends at 525.

As discussed above, one or more components of video encoder 20 of FIG.2A, video encoder 23 of FIG. 2B, video decoder 30 of FIG. 3A, or videodecoder 33 of FIG. 3B (e.g., inter-layer prediction unit 128 and/orinter-layer prediction unit 166) may be used to implement any of thetechniques discussed in the present disclosure, such as determiningwhether the EL picture is an IRAP picture, determining whether the ELpicture is at a splice point, and disallowing or allowing activation ofa new parameter set.

In the method 500, one or more of the blocks shown in FIG. 5 may beremoved (e.g., not performed) and/or the order in which the method isperformed may be switched. For example, although block 510 is shown inFIG. 5, it may be removed to simplify the coding process. Thus, theembodiments of the present disclosure are not limited to or by theexample shown in FIG. 5, and other variations may be implemented withoutdeparting from the spirit of this disclosure.

Constraints on Never-Activated Parameter Sets

In some coding schemes, there may be bitstream conformance constraints(e.g., constraints that may be determined to be applicable and thenadhered to by, for example, a coder) specified for active parameter sets(e.g., active PPS or active SPS), shown in italics:“pps_scaling_list_ref_layer_id specifies the value of the nuh_layer_idof the layer for which the active PPS is associated with the samescaling list data as the current PPS. The value ofpps_scaling_list_ref_layer_id shall be in the range of 0 to 62,inclusive. When avc_base_layer_flag is equal to 1, it is a requirementof bitstream conformance that pps_scaling_list_ref_layer_id shall begreater than 0. It is a requirement of bitstream conformance that, whena PPS with nuh_layer_id equal to nuhLayerIdA is active for a layer withnuh_layer_id equal to nuhLayerIdB and pps_infer_scaling_list_flag in thePPS is equal to 1, pps_infer_scaling_list_flag shall be equal to 0 forthe PPS that is active for the layer with nuh_layer_id equal topps_scaling_list_ref_layer_id. It is a requirement of bitstreamconformance that, when a PPS with nuh_layer_id equal to nuhLayerIdA isactive for a layer with nuh_layer_id equal to nuhLayerIdB, the layerwith nuh_layer_id equal to pps_scaling_list_ref_layer_id shall be adirect or indirect reference layer of the layer with nuh_layer_id equalto nuhLayerIdB.”

In some coding schemes, a parameter set that is never activated by anylayer may nonetheless be required to satisfy the following constraints,shown in italics: “All constraints that are expressed on therelationship between the values of the syntax elements and the values ofvariables derived from those syntax elements in VPSs, SPSs, and PPSs andother syntax elements are expressions of constraints that apply only tothe active VPS, the active SPS, and the active PPS. If any VPS RBSP, SPSRBSP, and PPS RBSP is present that is never activated in the bitstream,its syntax elements shall have values that would conform to thespecified constraints if it was activated by reference in an otherwiseconforming bitstream.”

However, for parameter sets such as VPS, SPS, PPS, etc. that are neveractivated, it may be difficult to check whether the first italicizedconstraints above are satisfied for parameter sets that are in abitstream but never activated, even considering the second italicizedconstraint. This is because even if a given parameter set satisfies theconstraints if activated for one layer, the same parameter set may failto satisfy the constraints if activated for another layer. Multipleparameter sets can be signaled for a single layer through the bitstream(e.g., prior to activation, regardless of whether they are activated ornot), so whether a particular bitstream is conformant cannot bedetermined unless those parameter sets are activated for one or morelayers.

Changes to Constraints on Never-Activated Parameter Sets

In some embodiments, the conformance check is excluded from thebitstream conformance check the syntax element of the never-activatedparameter set which bitstream conformance constraint depends on othersyntax elements from other parameter sets. The constraint discussedabove can be modified as follows: “If any VPS RBSP, SPS RBSP, and PPSRBSP is present that is never activated in the bitstream, syntaxelements of that particular parameter set RBSP shall have values thatwould conform to those specified constraints that are not dependent onthe value of any syntax element of another parameter set RBSP.”

In some embodiments, some particular syntax elements of thenever-activated parameter set can be skipped from the bitstreamconformance check according to some rule. For example, the conformancecheck checks the conformance constraint for the never-activatedparameter set only for the layer for which this parameter set issignaled. The constraint discussed above can be modified as follows: “Ifany VPS RBSP, SPS RBSP, and PPS RBSP is present that is never activatedin the bitstream, its syntax elements shall have values that wouldconform to the specified constraints if it was activated by referencewith the layer Id signaled in the parameter set in an otherwiseconforming bitstream.”

SPS Video Usability Information (VUI)

SPS VUI includes information such as sample aspect ratio, over scan,source video format (PAL/NTSC etc., sample value range, source colorformat), field/frame information, bitstream restrictions (includingcross-layer bitstream restrictions). Such information may includecross-layer bitstream restrictions, which may not be layer-specific butinstead apply to all layers. Thus, in some existing coding schemes, suchinformation may be repeated in each SPS.

In some embodiments, all SPS VUI information may be included in VPS VUI,and if for a particular layer any VUI parameter for an SPS must have adifferent value than that in the VPS VUI, the entire SPS VUI may bedirectly signaled in the SPS. Otherwise, the SPS does not contain VUIparameters and the VUI is inferred from the VPS.

Example changes of syntax and semantics that may be implemented tofacilitate the handling of the information described above, thefollowing changes may be made, where additions are shown in italics:

TABLE 1 example syntax of vps_vui( ) Descriptor vps_vui( ){  ... sps_vui_in_vps_flag u(1)  if( sps_vui_in_vps_flag )   vui_parameters( )}

The semantics for sps_vui_in_vps_flag may read as follows:“sps_vui_in_vps_flag equal to 1 specifies that the vui_parameters( )syntax structure is present in the VPS and applies to all SPSs thatrefer to the VPS and have sps_vui_from_vps_flag equal to 1.sps_vui_in_vps_flag equal to 0 specifies that the vui_parameters( )syntax structure is not present in the VPS. When vps_vui_present_flag isequal to 0, the value of sps_vui_in_vps_flag is inferred to be equal to0.”

TABLE 2 Example Syntax for seq_parameter_set_rbsp( ) Descriptorseq_parameter_set_rbsp( ) {  ...  if( nuh_layer_id > 0 )  sps_vui_from_vps_flag u(1)  if( !sps_vui_from_vps_flag )  vui_parameters_present_flag u(1)  if( vui_parameters_present_flag )  vui_parameters( )  sps_extension_flag u(1)  if( sps_extension_flag ) {  sps_extension( )   sps_extension2_flag u(1)   if( sps_extension2_flag)    while( more_rbsp_data( ) )     sps_extension_data_flag u(1)  } rbsp_trailing_bits( ) }

The semantics for sps_vui_from_vps_flag may read as follows:“sps_vui_from_vps_flag equal to 1 specifies that the vui_parameters( )syntax structure applicable to the SPS is inferred to be identical tothat in the VPS the SPS refers to. sps_vui_from_vps_flag equal to 0specifies that the vui_parameters( ) syntax structure applicable to theSPS is not inferred from the VPS the SPS refers to. When not present,the value of sps_vui_from_vps_flag is inferred to be equal to 0. Whensps_vui_in_vps_flag is equal to 0, the value of sps_vui_from_vps_flagshall be equal to 0.”

The semantics for vui_parameters_present_flag may read as follows:“vui_parameters_present_flag equal to 1 specifies that thevui_parameters( )) syntax structure as specified in Annex E is present.vui_parameters_present_flag equal to 0 specifies that thevui_parameters( ) syntax structure as specified in Annex E is notpresent. When not present, the value of vui_parameters_present_flag isinferred to be equal to 0.”

Other Considerations

Information and signals disclosed herein may be represented using any ofa variety of different technologies and techniques. For example, data,instructions, commands, information, signals, bits, symbols, and chipsthat may be referenced throughout the above description may berepresented by voltages, currents, electromagnetic waves, magneticfields or particles, optical fields or particles, or any combinationthereof.

The various illustrative logical blocks, modules, circuits, andalgorithm steps described in connection with the embodiments disclosedherein may be implemented as electronic hardware, computer software, orcombinations of both. To clearly illustrate this interchangeability ofhardware and software, various illustrative components, blocks, modules,circuits, and steps have been described above generally in terms oftheir functionality. Whether such functionality is implemented ashardware or software depends upon the particular application and designconstraints imposed on the overall system. Skilled artisans mayimplement the described functionality in varying ways for eachparticular application, but such implementation decisions should not beinterpreted as causing a departure from the scope of the presentinvention.

The techniques described herein may be implemented in hardware,software, firmware, or any combination thereof. Such techniques may beimplemented in any of a variety of devices such as general purposescomputers, wireless communication device handsets, or integrated circuitdevices having multiple uses including application in wirelesscommunication device handsets and other devices. Any features describedas modules or components may be implemented together in an integratedlogic device or separately as discrete but interoperable logic devices.If implemented in software, the techniques may be realized at least inpart by a computer-readable data storage medium comprising program codeincluding instructions that, when executed, performs one or more of themethods described above. The computer-readable data storage medium mayform part of a computer program product, which may include packagingmaterials. The computer-readable medium may comprise memory or datastorage media, such as random access memory (RAM) such as synchronousdynamic random access memory (SDRAM), read-only memory (ROM),non-volatile random access memory (NVRAM), electrically erasableprogrammable read-only memory (EEPROM), FLASH memory, magnetic oroptical data storage media, and the like. The techniques additionally,or alternatively, may be realized at least in part by acomputer-readable communication medium that carries or communicatesprogram code in the form of instructions or data structures and that canbe accessed, read, and/or executed by a computer, such as propagatedsignals or waves.

The program code may be executed by a processor, which may include oneor more processors, such as one or more digital signal processors(DSPs), general purpose microprocessors, an application specificintegrated circuits (ASICs), field programmable logic arrays (FPGAs), orother equivalent integrated or discrete logic circuitry. Such aprocessor may be configured to perform any of the techniques describedin this disclosure. A general purpose processor may be a microprocessor;but in the alternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration. Accordingly, the term “processor,” as used herein mayrefer to any of the foregoing structure, any combination of theforegoing structure, or any other structure or apparatus suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated software modules or hardware modules configured for encodingand decoding, or incorporated in a combined video encoder-decoder(CODEC). Also, the techniques could be fully implemented in one or morecircuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinter-operative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

Various embodiments of the invention have been described. These andother embodiments are within the scope of the following claims.

What is claimed is:
 1. An apparatus configured to code videoinformation, the apparatus comprising: a memory configured to storevideo data associated with a reference layer (RL) and an enhancementlayer (EL), the RL having an RL picture in a first access unit, and theEL having a first EL picture in the first access unit, wherein a secondEL picture that immediately precedes the first EL picture in codingorder is associated with a first set of parameters; and a processor incommunication with the memory, the processor configured to: determinethat the first EL picture is not an intra random access point (IRAP)picture; determine that a flag associated with the RL picture has avalue indicative of cross-layer random access skip pictures beingallowed to be output; based on the determination that the first ELpicture is not an IRAP picture and the flag associated with the RLpicture has a value indicative of cross-layer random access skippictures being allowed to be output, not activating a second set ofparameters that is different from the first set of parameters at thefirst EL picture such that the first set of parameters remains active atthe first EL picture; and encode or decode the first EL picture in abitstream based on the first set of parameters.
 2. The apparatus ofclaim 1, wherein the first EL picture does not immediately follow asplice point in coding order and the second EL picture does notimmediately precede a splice point in coding order.
 3. The apparatus ofclaim 1, wherein the processor is further configured to: determine thatthe first EL picture is indicated not to be an IRAP picture.
 4. Theapparatus of claim 1, wherein the processor is further configured todetermine that NoClrasOutputFlag included in the bitstream has a valueof
 0. 5. The apparatus of claim 1, wherein the processor is furtherconfigured to: in response to the determination that the first ELpicture is not an IRAP picture and the first access unit does notimmediately follow a splice point, determine that a second access unitthat follows the first access unit in coding order immediately follows asplice point, the second access unit including a third EL picture in theEL; and cause the EL to remain associated with the first set ofparameters at least until the third EL picture is at least partiallycoded.
 6. The apparatus of claim 1, wherein the processor is furtherconfigured to: cause, based on a determination that a third EL picturein the EL that follows the first EL picture in coding order is an IRAPpicture, the third EL picture to be associated with the second set ofparameters.
 7. The apparatus of claim 1, wherein the processor isfurther configured to: determine that a third EL picture in the EL thatfollows the first EL picture in coding order is an IRAP picture; andcause the EL to remain associated with the first set of parameters atleast until the third EL picture is at least partially coded.
 8. Theapparatus of claim 1, wherein the processor is further configured todetermine that the first EL picture is not an IRAP picture based atleast in part on header information associated with the first ELpicture.
 9. The apparatus of claim 1, wherein the processor is furtherconfigured to determine that the first EL picture is not an IRAP picturebased at least in part on a flag or a syntax element indicative ofwhether the first EL picture is an IRAP picture.
 10. The apparatus ofclaim 1, wherein the RL picture is associated with the first set ofparameters, and wherein the processor is further configured to cause theRL to remain associated with the first set of parameters at least untila new coded video sequence is at least partially processed.
 11. Theapparatus of claim 1, wherein the apparatus comprises at least one of anencoder configured to encode the first EL picture in the bitstream or adecoder configured to decode the first EL picture received in thebitstream.
 12. The apparatus of claim 1, wherein the apparatus comprisesa device selected from a group consisting of: a computer, a notebook, alaptop computer, a tablet computer, a set-top box, a telephone handset,a smart phone, a smart pad, a television, a camera, a display device, adigital media player, a video gaming console, and an in-car computer.13. A method of encoding video information, the method comprising:determining that a first enhancement layer (EL) picture in a firstaccess unit of an EL is not an intra random access point (IRAP) picture,wherein a second EL picture that immediately precedes the first ELpicture in coding order is associated with a first set of parameters;determining that a flag associated with the RL picture has a valueindicative of cross-layer random access skip pictures being allowed tobe output; based on determining that the first EL picture is not an IRAPpicture and the flag associated with the RL picture has a valueindicative of cross-layer random access skip pictures being allowed tobe output, not activating a second set of parameters that is differentfrom the first set of parameters at the first EL picture such that thefirst set of parameters remains active at the first EL picture; andencoding, based on the first set of parameters, the first EL picture ina bitstream.
 14. The method of claim 13, wherein the first EL picturedoes not immediately follow a splice point in coding order and thesecond EL picture does not immediately precede a splice point in codingorder.
 15. The method of claim 13, further comprising: determining thatthe first EL picture is indicated not to be an IRAP picture.
 16. Themethod of claim 13, further comprising determining thatNoClrasOutputFlag included in the bitstream has a value of
 0. 17. Themethod of claim 13, further comprising: in response to determining thatthe first EL picture is not an RAP picture and the first access unitdoes not immediately follow a splice point, determining that a secondaccess unit that follows the first access unit in coding orderimmediately follows a splice point, the second access unit including athird EL picture in the EL; and causing the EL to remain associated withthe first set of parameters at least until the third EL picture is atleast partially coded.
 18. The method of claim 13, further comprisingcausing, based on a determination that a third EL picture in the EL thatfollows the first EL picture in coding order is an RAP picture, thethird EL picture to be associated with the second set of parameters. 19.The method of claim 13, further comprising: determining that a third ELpicture in the EL that follows the first EL picture in coding order isan IRAP picture; and causing the EL to remain associated with the firstset of parameters at least until the third EL picture is at leastpartially coded.
 20. The method of claim 13, further comprisingdetermining that the first EL picture is not an IRAP picture based atleast in part on header information associated with the first ELpicture.
 21. The method of claim 13, further comprising determining thatthe first EL picture is not an IRAP picture based at least in part on aflag or a syntax element indicative of whether the first EL picture isan IRAP picture.
 22. The method of claim 13, further comprising causingthe RL that is associated with the first set of parameters to remainassociated with the first set of parameters at least until a new codedvideo sequence is at least partially processed.
 23. Non-transitoryphysical computer storage comprising code that, when executed, causes anapparatus to: store video data associated with a reference layer (RL)and an enhancement layer (EL), the RL having an RL picture in a firstaccess unit, and the EL having a first EL picture in the first accessunit, wherein a second EL picture that immediately precedes the first ELpicture in coding order is associated with a first set of parameters;determine that the first EL picture is not an intra random access point(IRAP) picture; determine that a flag associated with the RL picture hasa value indicative of cross-layer random access skip pictures beingallowed to be output; based on the determination that the first ELpicture is not an IRAP picture and the flag associated with the RLpicture has a value indicative of cross-layer random access skippictures being allowed to be output, not activating a second set ofparameters that is different from the first set of parameters at thefirst EL picture such that the first set of parameters remains active atthe first EL picture; and encode or decode the first EL picture in abitstream based on the first set of parameters.
 24. The non-transitoryphysical computer storage of claim 23, wherein the first EL picture doesnot immediately follow a splice point in coding order and the second ELpicture does not immediately precede a splice point in coding order. 25.The non-transitory physical computer storage of claim 23, wherein theprocess further comprises: in response to the determination that thefirst EL picture is not an IRAP picture and the first access unit doesnot immediately follow a splice point, determining that a second accessunit that follows the first access unit in coding order immediatelyfollows a splice point, the second access unit including a third ELpicture in the EL; and causing the EL to remain associated with thefirst set of parameters at least until the third EL picture is at leastpartially coded.
 26. A video coding device configured to code videoinformation, the video coding device comprising: means for storing videodata associated with a reference layer (RL) and an enhancement layer(EL), the RL having an RL picture in a first access unit, and the ELhaving a first EL picture in the first access unit, wherein a second ELpicture that immediately precedes the first EL picture in coding orderis associated with a first set of parameters; means for determining thatthe first EL picture is not an intra random access point (IRAP) picture;means for determining that a flag associated with the RL picture has avalue indicative of cross-layer random access skip pictures beingallowed to be output; means for based on the determination that thefirst EL picture is not an IRAP picture and the flag associated with theRL picture has a value indicative of cross-layer random access skippictures being allowed to be output, not activating a second set ofparameters that is different from the first set of parameters at thefirst EL picture such that the first set of parameters remains active atthe first EL picture; and means for encoding or decoding the first ELpicture in a bitstream based on the first set of parameters.
 27. Thevideo coding device of claim 26, wherein the first EL picture does notimmediately follow a splice point in coding order and the second ELpicture does not immediately precede a splice point in coding order. 28.The video coding device of claim 26, further comprising: means fordetermining, in response to the determination that the first EL pictureis not an IRAP picture and that the first access unit does notimmediately follow a splice point, that a second access unit thatfollows the first access unit in coding order immediately follows asplice point, the second access unit including a third EL picture in theEL; and means for causing the EL to remain associated with the first setof parameters at least until the third EL picture is at least partiallycoded.